One potential way to increase photovoltaic efficiency is to take advantage of hot-carriers. Nanocrystal based solar cells aim to take advantage of hot-carrier capture to boost device performance. The crucial parameter for gauging a given nanocrystal material for this application is the electron-phonon coupling. The electron-phonon coupling will dictate the thermalization time of hot-carriers. In this study we demonstrate a method of quantifying the electron-phonon coupling in semiconductor nanocrystals. By employing ultrafast transient absorption spectroscopy with temporal pulse shaping, we manipulate coherent phonons in CdTe_{1-x}Se_{x} nanocrystals to quantify the efficiency of the electron-phonon coupling. The Raman active longitudinal optical phonon (LO) modes were excited and probed as a function of time. Using a temporal pulse shaper, we were able to control pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe_{1-x}Se_{x} nanocrystals, and estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode which is the dominant thermalization pathway for the hot-electrons in this system.
{"title":"Quantifying energy transfer in semiconductor nanocrystals using coherent phonon manipulation and ultrafast spectroscopy (Presentation Recording)","authors":"Bryan T. Spann, Xianfan Xu","doi":"10.1117/12.2186831","DOIUrl":"https://doi.org/10.1117/12.2186831","url":null,"abstract":"One potential way to increase photovoltaic efficiency is to take advantage of hot-carriers. Nanocrystal based solar cells aim to take advantage of hot-carrier capture to boost device performance. The crucial parameter for gauging a given nanocrystal material for this application is the electron-phonon coupling. The electron-phonon coupling will dictate the thermalization time of hot-carriers. In this study we demonstrate a method of quantifying the electron-phonon coupling in semiconductor nanocrystals. By employing ultrafast transient absorption spectroscopy with temporal pulse shaping, we manipulate coherent phonons in CdTe_{1-x}Se_{x} nanocrystals to quantify the efficiency of the electron-phonon coupling. The Raman active longitudinal optical phonon (LO) modes were excited and probed as a function of time. Using a temporal pulse shaper, we were able to control pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe_{1-x}Se_{x} nanocrystals, and estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode which is the dominant thermalization pathway for the hot-electrons in this system.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125966778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carina Bronnbauer, K. Forberich, Fei Guo, N. Gasparini, C. Brabec
Building integrated thin film solar cells are a strategy for future eco-friendly power generation. Such solar cells have to be semi-transparent, long-term stable and show the potential to be fabricated by a low-cost production process. Organic photovoltaics are a potential candidate because an absorber material with its main absorption in the infrared spectral region where the human eye is not sensitive can be chosen. We can increase the number of absorbed photons, at the same time, keep the transparency almost constant by using a dielectric, wavelength-selective mirror. The mirror reflects only in the absorption regime of the active layer material and shows high transparencies in the spectral region around 550 nm where the human eye is most sensitive. We doctor bladed a fully solution processed dielectric mirror at low temperatures below 80 °C. Both inks, which are printed alternatingly are based on nanoparticles and have a refractive index of 1.29 or 1.98, respectively, at 500 nm. The position and the intensity of the main reflection peak can be easily shifted and thus adjusted to the solar cell absorption spectrum. Eventually, the dielectric mirror was combined with different organic solar cells. For instance, the current increases by 20.6 % while the transparency decreases by 23.7 % for the low band gap absorber DPP and silver nanowires as top electrode. Moreover we proved via experiment and optical simulations, that a variation of the active layer thickness and the position of the main reflection peak affect the transparency and the increase in current.
{"title":"Efficiency enhancement of semitransparent organic solar cells by using printed dielectric mirrors (Presentation Recording)","authors":"Carina Bronnbauer, K. Forberich, Fei Guo, N. Gasparini, C. Brabec","doi":"10.1117/12.2188263","DOIUrl":"https://doi.org/10.1117/12.2188263","url":null,"abstract":"Building integrated thin film solar cells are a strategy for future eco-friendly power generation. Such solar cells have to be semi-transparent, long-term stable and show the potential to be fabricated by a low-cost production process. Organic photovoltaics are a potential candidate because an absorber material with its main absorption in the infrared spectral region where the human eye is not sensitive can be chosen. We can increase the number of absorbed photons, at the same time, keep the transparency almost constant by using a dielectric, wavelength-selective mirror. The mirror reflects only in the absorption regime of the active layer material and shows high transparencies in the spectral region around 550 nm where the human eye is most sensitive. We doctor bladed a fully solution processed dielectric mirror at low temperatures below 80 °C. Both inks, which are printed alternatingly are based on nanoparticles and have a refractive index of 1.29 or 1.98, respectively, at 500 nm. The position and the intensity of the main reflection peak can be easily shifted and thus adjusted to the solar cell absorption spectrum. Eventually, the dielectric mirror was combined with different organic solar cells. For instance, the current increases by 20.6 % while the transparency decreases by 23.7 % for the low band gap absorber DPP and silver nanowires as top electrode. Moreover we proved via experiment and optical simulations, that a variation of the active layer thickness and the position of the main reflection peak affect the transparency and the increase in current.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122837296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Busani, O. Lavrova, M. Erdman, Julio A. Martinez, N. Dawson
We designed and studied a radial junction composed by a photovoltaic and thermoelectric array based on ZnO and CdTe nanowires surrounded by an absorbing organic self assembled in order to efficiently convert UV-visible and IR energy into electricity. The hot anode of n-type ZnO nanowires was fabricated using a thermal process on pre-seeded layer and results to be crystalline with a transmittance up to 92 % and a bandgap of ~ 3.32 eV. Conductivity measurements reveal diode-like behavior for the ZnO nanowires. The organic layer was deposited between the anode and cathode at room temperature The organic layer is composed of oppositely charged porphyrin metal (Zn(II) and Sn(IV)(OH)2) derivatives that are separately water soluble, but when combined form a virtually insoluble solid. The electron donor/acceptor properties (energy levels, band gaps) of the solid can be controlled by the choice of metals and the nature of the peripheral substituent groups of the porphyrin ring. A defect free sub nanometer deposition was achieved using a layer-by-layer deposition onto both ZnO and Bi2Te3 nanowires. The highly thermoelectric structure, which acts as a cold cathode, is composed of p-type Bi2Te3 nanowires with a thermoelectric efficiency (ZT) between ~0.7 to 1, values that are twice that expected for bulk Bi2Te3. Optoelectronic and structural properties shows that with 6 nm of organic layer it is possible to form a 3% efficient solar device with an enhanced thermo electric effected with a temperature gradient of 300 C.
{"title":"Monolithically self-assembled organic active materials integrated with thermoelectric for large spectrum solar harvesting system (Presentation Recording)","authors":"T. Busani, O. Lavrova, M. Erdman, Julio A. Martinez, N. Dawson","doi":"10.1117/12.2188897","DOIUrl":"https://doi.org/10.1117/12.2188897","url":null,"abstract":"We designed and studied a radial junction composed by a photovoltaic and thermoelectric array based on ZnO and CdTe nanowires surrounded by an absorbing organic self assembled in order to efficiently convert UV-visible and IR energy into electricity. The hot anode of n-type ZnO nanowires was fabricated using a thermal process on pre-seeded layer and results to be crystalline with a transmittance up to 92 % and a bandgap of ~ 3.32 eV. Conductivity measurements reveal diode-like behavior for the ZnO nanowires. The organic layer was deposited between the anode and cathode at room temperature The organic layer is composed of oppositely charged porphyrin metal (Zn(II) and Sn(IV)(OH)2) derivatives that are separately water soluble, but when combined form a virtually insoluble solid. The electron donor/acceptor properties (energy levels, band gaps) of the solid can be controlled by the choice of metals and the nature of the peripheral substituent groups of the porphyrin ring. A defect free sub nanometer deposition was achieved using a layer-by-layer deposition onto both ZnO and Bi2Te3 nanowires. The highly thermoelectric structure, which acts as a cold cathode, is composed of p-type Bi2Te3 nanowires with a thermoelectric efficiency (ZT) between ~0.7 to 1, values that are twice that expected for bulk Bi2Te3. Optoelectronic and structural properties shows that with 6 nm of organic layer it is possible to form a 3% efficient solar device with an enhanced thermo electric effected with a temperature gradient of 300 C.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126004291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
With the advent of X-ray free electron lasers and table-top high-harmonic-generation X-ray sources, we can now explore changes in electronic structure on ultrafast time scales -- at or less than 1ps. Transient X-ray spectroscopy of this kind provides a direct probe of relevant electronic levels related to photoinitiated processes and associated interfacial electron transfer as the initial step in solar energy conversion. However, the interpretation of such spectra is typically fraught with difficulty, especially since we rarely have access to spectral standards for nonequilibrium states. To this end, direct first-principles simulations of X-ray absorption spectra can provide the necessary connection between measurements and reliable models of the atomic and electronic structure. We present examples of modeling excited states of materials interfaces relevant to solar harvesting and their corresponding X-ray spectra in either photoemission or absorption modalities. In this way, we can establish particular electron transfer mechanisms to reveal detailed working principles of materials systems in solar applications and provide insight for improved efficiency.
{"title":"Exploring the time-scale of photo-initiated interfacial electron transfer through first-principles interpretation of ultrafast X-ray spectroscopy (Presentation Recording)","authors":"D. Prendergast, S. Pemmaraju","doi":"10.1117/12.2190444","DOIUrl":"https://doi.org/10.1117/12.2190444","url":null,"abstract":"With the advent of X-ray free electron lasers and table-top high-harmonic-generation X-ray sources, we can now explore changes in electronic structure on ultrafast time scales -- at or less than 1ps. Transient X-ray spectroscopy of this kind provides a direct probe of relevant electronic levels related to photoinitiated processes and associated interfacial electron transfer as the initial step in solar energy conversion. However, the interpretation of such spectra is typically fraught with difficulty, especially since we rarely have access to spectral standards for nonequilibrium states. To this end, direct first-principles simulations of X-ray absorption spectra can provide the necessary connection between measurements and reliable models of the atomic and electronic structure. We present examples of modeling excited states of materials interfaces relevant to solar harvesting and their corresponding X-ray spectra in either photoemission or absorption modalities. In this way, we can establish particular electron transfer mechanisms to reveal detailed working principles of materials systems in solar applications and provide insight for improved efficiency.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129253006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A study of the photovoltaic properties of the GaAs-based solar cells with InGaAs quantum wire had been conducted. The research included the investigation of the photovoltage rise and decay transients, spectral photovoltage dependences at different temperatures. The objects investigated were GaAs-based solar cells with InGaAs quantum wire (QWR) embedded into space-charge-region of p-i-n junction. Samples with different In content and size of InGaAs nanoobjects had been created using molecular beam epitaxy. Unlike the reference cell, the ones containing the InGaAs QWR had shown higher sensitivity in the energy range 1.2 - 1.38 eV. This is caused by the spatial separation of electron-hole (e-h) pairs excited in the QWR due to band-to-band transition. Under selective excitation of the e-h pairs only in the InGaAs quantum wire the photovoltage rise transient is slower compared to the e-h generation in GaAs. This effect is explained by charge carriers release from the InGaAs quantum well into delocalized states of the surrounding GaAs. It was determined that the InGaAs quantum wires increase the recombination rate of the non-equilibrium carriers in the temperature range 80 to 290 K, which means that the quantum wires are the additional recombination centers.
{"title":"Photovoltage transients in GaAs/InGaAs solar cells (Presentation Recording)","authors":"Roman Holubenko, A. Yakovliev, S. Kondratenko","doi":"10.1117/12.2187066","DOIUrl":"https://doi.org/10.1117/12.2187066","url":null,"abstract":"A study of the photovoltaic properties of the GaAs-based solar cells with InGaAs quantum wire had been conducted. The research included the investigation of the photovoltage rise and decay transients, spectral photovoltage dependences at different temperatures. The objects investigated were GaAs-based solar cells with InGaAs quantum wire (QWR) embedded into space-charge-region of p-i-n junction. Samples with different In content and size of InGaAs nanoobjects had been created using molecular beam epitaxy. Unlike the reference cell, the ones containing the InGaAs QWR had shown higher sensitivity in the energy range 1.2 - 1.38 eV. This is caused by the spatial separation of electron-hole (e-h) pairs excited in the QWR due to band-to-band transition. Under selective excitation of the e-h pairs only in the InGaAs quantum wire the photovoltage rise transient is slower compared to the e-h generation in GaAs. This effect is explained by charge carriers release from the InGaAs quantum well into delocalized states of the surrounding GaAs. It was determined that the InGaAs quantum wires increase the recombination rate of the non-equilibrium carriers in the temperature range 80 to 290 K, which means that the quantum wires are the additional recombination centers.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129456929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
I. Ivanova, Tarek A. Kandiel, A. Hakki, R. Dillert, D. Bahnemann
To solve the global energy and environmental issues highly efficient systems for solar energy conversion and storage are needed. One of them involves the photocatalytic conversion of solar energy into the storable fuel molecular hydrogen via the water splitting process utilizing metal-oxide semiconductors as catalysts. Since photocatalytic water splitting is still a rather poorly understood reaction, fundamental research in this field is required. Herein, the photocatalytic activity for water splitting was investigated utilizing La-doped NaTaO3 as a model photocatalyst. The activity of La-doped NaTaO3 was assessed by the determination of the overall quantum yield of molecular hydrogen and molecular oxygen evolution. In pure water La-doped NaTaO3 exhibits rather poor activity for the photocatalytic H2 evolution whereby no O2 was detected. To enhance the photocatalytic activity the surface of La-doped NaTaO3 was modified with various cocatalysts including noble metals (Pt, Au and Rh) and metal oxides (NiO, CuO, CoO, AgO and RuO2). The photocatalytic activity was evaluated in pure water, in aqueous methanol solution, and in aqueous silver nitrate solution. The results reveal that cocatalysts such as RuO2 or CuO exhibiting the highest catalytic activity for H2 evolution from pure water, possess, however, the lowest activity for O2 evolution from aqueous silver nitrate solution. La-doped NaTaO3 modified with Pt shows the highest quantum yield of 33 % with respect to the H2 evolution in the presence of methanol. To clarify the role of methanol in such a photocatalytic system, long-term investigations and isotopic studies were performed. The underlying mechanisms of methanol oxidation were elucidated.
{"title":"Photocatalytic evolution of molecular hydrogen and oxygen over La-doped NaTaO3 particles: Effect of different cocatalysts (Presentation Recording)","authors":"I. Ivanova, Tarek A. Kandiel, A. Hakki, R. Dillert, D. Bahnemann","doi":"10.1117/12.2186561","DOIUrl":"https://doi.org/10.1117/12.2186561","url":null,"abstract":"To solve the global energy and environmental issues highly efficient systems for solar energy conversion and storage are needed. One of them involves the photocatalytic conversion of solar energy into the storable fuel molecular hydrogen via the water splitting process utilizing metal-oxide semiconductors as catalysts. Since photocatalytic water splitting is still a rather poorly understood reaction, fundamental research in this field is required. Herein, the photocatalytic activity for water splitting was investigated utilizing La-doped NaTaO3 as a model photocatalyst. The activity of La-doped NaTaO3 was assessed by the determination of the overall quantum yield of molecular hydrogen and molecular oxygen evolution. In pure water La-doped NaTaO3 exhibits rather poor activity for the photocatalytic H2 evolution whereby no O2 was detected. To enhance the photocatalytic activity the surface of La-doped NaTaO3 was modified with various cocatalysts including noble metals (Pt, Au and Rh) and metal oxides (NiO, CuO, CoO, AgO and RuO2). The photocatalytic activity was evaluated in pure water, in aqueous methanol solution, and in aqueous silver nitrate solution. The results reveal that cocatalysts such as RuO2 or CuO exhibiting the highest catalytic activity for H2 evolution from pure water, possess, however, the lowest activity for O2 evolution from aqueous silver nitrate solution. La-doped NaTaO3 modified with Pt shows the highest quantum yield of 33 % with respect to the H2 evolution in the presence of methanol. To clarify the role of methanol in such a photocatalytic system, long-term investigations and isotopic studies were performed. The underlying mechanisms of methanol oxidation were elucidated.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129567428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recently prices of photovoltaic (PV) systems have been reduced considerably and may continue to be reduced making them attractive. If these systems provide electricity over the stipulated warranty period, it would be possible attain socket parity within the next few years. Current photovoltaic module qualifications tests help in minimizing infant mortality but do not guarantee useful lifetime over the warranty period. The PV Module Quality Assurance Task Force (PVQAT) is trying to formulate accelerated tests that will be useful towards achieving the ultimate goal of assuring useful lifetime over the warranty period as well as to assure manufacturing quality. Unfortunately, assuring the manufacturing quality may require 24/7 presence. Alternatively, collecting data on the performance of fielded systems would assist in assuring manufacturing quality. Here PV systems installed by home-owners and small businesses can constitute as an important untapped source of data. The volunteer group, PV - Reliable, Safe and Sustainable Quality! (PVRessQ!) is providing valuable service to small PV system owners. Photovoltaic Reliability Group (PVRG) is initiating activities in USA and Brazil to assist home owners and small businesses in monitoring photovoltaic (PV) module performance and enforcing warranty. It will work in collaboration with small PV system owners, consumer protection agencies. Brazil is endowed with excellent solar irradiance making it attractive for installation of PV systems. Participating owners of small PV systems would instruct inverter manufacturers to copy the daily e-mails to PVRG and as necessary, will authorize the PVRG to carry out review of PV systems. The presentation will consist of overall activities of PVRG in USA and Brazil.
{"title":"Photovoltaic Reliability Group activities in USA and Brazil (Presentation Recording)","authors":"N. Dhere, L. R. O. Cruz","doi":"10.1117/12.2187767","DOIUrl":"https://doi.org/10.1117/12.2187767","url":null,"abstract":"Recently prices of photovoltaic (PV) systems have been reduced considerably and may continue to be reduced making them attractive. If these systems provide electricity over the stipulated warranty period, it would be possible attain socket parity within the next few years. Current photovoltaic module qualifications tests help in minimizing infant mortality but do not guarantee useful lifetime over the warranty period. The PV Module Quality Assurance Task Force (PVQAT) is trying to formulate accelerated tests that will be useful towards achieving the ultimate goal of assuring useful lifetime over the warranty period as well as to assure manufacturing quality. Unfortunately, assuring the manufacturing quality may require 24/7 presence. Alternatively, collecting data on the performance of fielded systems would assist in assuring manufacturing quality. Here PV systems installed by home-owners and small businesses can constitute as an important untapped source of data. The volunteer group, PV - Reliable, Safe and Sustainable Quality! (PVRessQ!) is providing valuable service to small PV system owners. Photovoltaic Reliability Group (PVRG) is initiating activities in USA and Brazil to assist home owners and small businesses in monitoring photovoltaic (PV) module performance and enforcing warranty. It will work in collaboration with small PV system owners, consumer protection agencies. Brazil is endowed with excellent solar irradiance making it attractive for installation of PV systems. Participating owners of small PV systems would instruct inverter manufacturers to copy the daily e-mails to PVRG and as necessary, will authorize the PVRG to carry out review of PV systems. The presentation will consist of overall activities of PVRG in USA and Brazil.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116353534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emre Yassitepe, O. Voznyy, E. Sargent, A. Nogueira
Colloidal quantum dot heterojunction thin film solar cells (CQD-TFSC) utilize facile thin film deposition methods and promise high photon conversion efficiencies (PCE) to cost ratio which is highly desired for commercialization. So far, surface passivated PbS CQD-TFSCs show the highest PCE results, reaching 9.2% with good stability. Among other potential candidates, CuInSe2 CQDs stand out as a non-toxic material with high potential for performance, judging on bulk Cu(Ga,In)(S,Se)2 TFSCs reaching 20% PCE, with high stability. CuInSe2 CQDs has advantage over bulk films, mainly the much less expensive manufacturing cost of uniform deposition on large areas. Ga is known to cause phase separation in the bulk CIGS system. In a CQD form, CuInSe2 band gap can be tuned between 1 to 1.6 eV by quantum confinement without need for Ga and this eliminates the phase separation issue. Within our best knowledge, there are no reports on surface trap passivated CuInSe2 CQD-TFSCs. However Cu(In,Ga)(S,Se)2 colloidal particles were cast in thin film form and fused to form bulk-like crystals by various annealing conditions for solar cell devices. In this work, we investigated well-passivated CuInSe2 CQDs on n-type TiO2 and ZnO layers to form depleted heterojunction structure. We prepared luminescent CuInSe2 CQDs by synthetic wet chemistry methods and passivated the surface with 3-mercaptopropionic acid or tetrabutylammonium iodide using solid-state ligand exchange. X-ray photoelectron spectroscopy was used to confirm the ligand boding and surface coverage of the quantum dots. We will present the effect of synthesis and thin film preparation conditions on the solar cell device performance
{"title":"Surface passivated colloidal CuIn(S,Se)2 quantum dots for quantum dot heterojunction solar cells (Presentation Recording)","authors":"Emre Yassitepe, O. Voznyy, E. Sargent, A. Nogueira","doi":"10.1117/12.2188567","DOIUrl":"https://doi.org/10.1117/12.2188567","url":null,"abstract":"Colloidal quantum dot heterojunction thin film solar cells (CQD-TFSC) utilize facile thin film deposition methods and promise high photon conversion efficiencies (PCE) to cost ratio which is highly desired for commercialization. So far, surface passivated PbS CQD-TFSCs show the highest PCE results, reaching 9.2% with good stability. Among other potential candidates, CuInSe2 CQDs stand out as a non-toxic material with high potential for performance, judging on bulk Cu(Ga,In)(S,Se)2 TFSCs reaching 20% PCE, with high stability. CuInSe2 CQDs has advantage over bulk films, mainly the much less expensive manufacturing cost of uniform deposition on large areas. Ga is known to cause phase separation in the bulk CIGS system. In a CQD form, CuInSe2 band gap can be tuned between 1 to 1.6 eV by quantum confinement without need for Ga and this eliminates the phase separation issue. Within our best knowledge, there are no reports on surface trap passivated CuInSe2 CQD-TFSCs. However Cu(In,Ga)(S,Se)2 colloidal particles were cast in thin film form and fused to form bulk-like crystals by various annealing conditions for solar cell devices. In this work, we investigated well-passivated CuInSe2 CQDs on n-type TiO2 and ZnO layers to form depleted heterojunction structure. We prepared luminescent CuInSe2 CQDs by synthetic wet chemistry methods and passivated the surface with 3-mercaptopropionic acid or tetrabutylammonium iodide using solid-state ligand exchange. X-ray photoelectron spectroscopy was used to confirm the ligand boding and surface coverage of the quantum dots. We will present the effect of synthesis and thin film preparation conditions on the solar cell device performance","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116806703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mastery over the surface of a nanocrystal enables control of its properties in molecular adsorption and activation, and enhances its usefulness for catalytic applications. On the other hand, hybrid systems based on semiconductors and noble metals may exhibit improved performance in photocatalysis such as water splitting, mainly determined by the efficiency in generating carriers. In the systems, perfect interface is certainly the key to efficient carrier separation and transport. Taken together, the surface and interface modulation holds the key to materials design for photocatalytic applications. Here, we will demonstrate several different approaches to designing nanocrystal-based systems with improved photocatalytic performance. For instance, a semiconductor-metal-graphene design has been implemented to efficiently extract photoexcited electrons through the graphene nanosheets, separating electron-hole pairs. Ultrafast spectroscopy characterizations exclusively demonstrate that the charge recombination occurring at interfacial defects can be substantially avoided, enabling superior efficiency in water splitting. It is anticipated that this series of works open a new window to rationally designing hybrid systems for photo-induced applications.
{"title":"Design of inorganic hybrid structures for photocatalytic energy conversion (Presentation Recording)","authors":"Y. Xiong","doi":"10.1117/12.2180038","DOIUrl":"https://doi.org/10.1117/12.2180038","url":null,"abstract":"Mastery over the surface of a nanocrystal enables control of its properties in molecular adsorption and activation, and enhances its usefulness for catalytic applications. On the other hand, hybrid systems based on semiconductors and noble metals may exhibit improved performance in photocatalysis such as water splitting, mainly determined by the efficiency in generating carriers. In the systems, perfect interface is certainly the key to efficient carrier separation and transport. Taken together, the surface and interface modulation holds the key to materials design for photocatalytic applications. Here, we will demonstrate several different approaches to designing nanocrystal-based systems with improved photocatalytic performance. For instance, a semiconductor-metal-graphene design has been implemented to efficiently extract photoexcited electrons through the graphene nanosheets, separating electron-hole pairs. Ultrafast spectroscopy characterizations exclusively demonstrate that the charge recombination occurring at interfacial defects can be substantially avoided, enabling superior efficiency in water splitting. It is anticipated that this series of works open a new window to rationally designing hybrid systems for photo-induced applications.","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128624704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Tennyson, J. Garrett, J. Frantz, J. Myers, R. Bekele, J. Sanghera, J. Munday, M. Leite
The electrical characteristics of thin-film compound semiconductor solar cells have been successfully probed by scanning probe microscopy. Nevertheless, a direct relationship between the measured signals and the figures of merit that define the device performance is still missing. Here we present a novel method to image and spatially resolve the Voc of solar cells with truly nanoscale resolution (<100 nm), based on a variant of illuminated Kelvin probe force microscopy (KPFM) [1]. We map the Voc by measuring the difference between the contact potential difference under illumination and in the dark, which is equal to the photo-generated voltage of the device (and is proportional to the Fermi level splitting). We complement our new metrology by applying scanning photocurrent microscopy using near-field scanning microscopy (NSOM) probes as a local source of excitation to image local variations in Jsc within the material, also with nanoscale resolution. Further, we spatially and spectrally resolve the external quantum efficiency (EQE) within the devices, also with nanoscale resolution, while mimicking the power density operation conditions of real devices [2]. Combined, these new tools provide a complete picture of the local optoelectric characteristics of PV devices, including an indirect measurement of the centers for non-radiative recombination, and a direct mapping of the local collection properties of the material, respectively. We apply our novel metrology to polycrystalline solar cells, where we find Voc local variations of >200 mV. [1] E.M. Tennyson et al., Nature Commun., in review; [2] M.S. Leite et al., ACS Nano. 11, 11883 (2014).
{"title":"A novel method for mapping open-circuit voltage in solar cells with nanoscale resolution (Presentation Recording)","authors":"E. Tennyson, J. Garrett, J. Frantz, J. Myers, R. Bekele, J. Sanghera, J. Munday, M. Leite","doi":"10.1117/12.2187581","DOIUrl":"https://doi.org/10.1117/12.2187581","url":null,"abstract":"The electrical characteristics of thin-film compound semiconductor solar cells have been successfully probed by scanning probe microscopy. Nevertheless, a direct relationship between the measured signals and the figures of merit that define the device performance is still missing. Here we present a novel method to image and spatially resolve the Voc of solar cells with truly nanoscale resolution (<100 nm), based on a variant of illuminated Kelvin probe force microscopy (KPFM) [1]. We map the Voc by measuring the difference between the contact potential difference under illumination and in the dark, which is equal to the photo-generated voltage of the device (and is proportional to the Fermi level splitting). We complement our new metrology by applying scanning photocurrent microscopy using near-field scanning microscopy (NSOM) probes as a local source of excitation to image local variations in Jsc within the material, also with nanoscale resolution. Further, we spatially and spectrally resolve the external quantum efficiency (EQE) within the devices, also with nanoscale resolution, while mimicking the power density operation conditions of real devices [2]. Combined, these new tools provide a complete picture of the local optoelectric characteristics of PV devices, including an indirect measurement of the centers for non-radiative recombination, and a direct mapping of the local collection properties of the material, respectively. We apply our novel metrology to polycrystalline solar cells, where we find Voc local variations of >200 mV. [1] E.M. Tennyson et al., Nature Commun., in review; [2] M.S. Leite et al., ACS Nano. 11, 11883 (2014).","PeriodicalId":142821,"journal":{"name":"SPIE Optics + Photonics for Sustainable Energy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115764135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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