Solar Energy Materials and Solar Cells最新文献

To improve the Photovoltaic (PV) module design for desert climates, it is important to understand the typical failure mechanism observed and the main cause of failure. This paper reports on PV backsheet degradation in desert climates. Field inspections reveal that backsheet degradation was found to be one of the most frequent PV system failures observed at the Outdoor Test Facility (OTF) in addition to hotspots, snail trails, and encapsulant yellowing. Degradation of two different polyamide (PA) and two different polyethylene terephthalate (PET) backsheets were investigated in real outdoor testing conditions. The observation of material changes due to degradation was studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Backsheet crack initiation, propagation, and chalking were monitored. We found that the embrittlement of the PA-based and PET-backsheet materials is caused by a combination of prolonged exposure to high ultraviolet (UV) radiation, high operating temperature cycling, and relative humidity resulting in cracking of the top UV-blocker layer and subsequent chemical and physical degradation of the underlying layers. The PET-2 showed only chalking powder with no backsheet cracking, which indicates an early stage of backsheet degradation. The green spot observed on the PA backsheet was found to be antlerite (greenish hydrous copper sulfate mineral Cu₃ (SO₄) (OH) ₄) resulting from the reaction of the chalking and the solar cell interconnections.

This study introduces a pioneering machine learning (ML)-based methodology to characterise two-level defects in the bulk of silicon wafers. Bulk defects have a critical impact on the efficiency of silicon solar cells. By identifying the specific parameters of these defects, namely, their energy levels and capture cross-sections, researchers can devise strategies to mitigate their effects. It is often assumed that bulk defects are single-level defects following the Shockley-Read-Hall recombination statistics. However, two-level defects or even multi-level defects are common as well. At present, it is challenging to distinguish between single-level defects and two-level defects, and to extract the parameters of a two-level defect. This study proposes an ML-based approach to distinguish between one- and two-level defects based on temperature- and injection-dependent lifetime spectroscopy with an accuracy above 90 %. Furthermore, if the defect is identified as a two-level defect, this study presents another ML method to extract its defect parameters, with a correlation coefficient above 0.9 for the energy levels.

This study reports on the electronic properties of industrial phosphorus-doped n-type silicon ingots for photovoltaic applications grown using the Recharged Czochralski method. The electronic quality is assessed via carrier lifetime measurements, both directly on the ingots and on passivated wafers, and via implied open-circuit (${iV}_{OC}$), and implied maximum power point ($i{V}_{MPP}$) voltages. The wafers are studied in the as-grown state, and after various high temperature steps, including Tabula Rasa, phosphorus diffusion gettering, and boron diffusion. The material exhibited very high bulk quality, with bulk lifetimes up to $8\text{ms}$ at an injection level of $5\times {10}^{14}{\text{cm}}^{-3}$, and with ${iV}_{OC}$ (1-sun) values up to $750\text{mV}$, prior to any high temperature processing. A Tabula Rasa step did not significantly improve the wafer quality, indicating a low presence of oxygen-related defects in this material, consistent with the low interstitial oxygen content of below $5\times {10}^{17}{\text{cm}}^{-3}$. However, phosphorus diffusion gettering improved the wafer quality, especially towards the tail end of each ingot, and at lower injection levels near maximum power point. Phosphorus diffusion gettering increased the ${iV}_{OC}$ (1-sun) of the wafers by around $5\text{mV}$, approaching the Auger limit. Additionally, a boron diffusion step had minimal impact on the bulk lifetimes. Overall, our findings suggest that these RCz-grown n-type wafers exhibit very high quality, approaching the Auger limit near open-circuit, and are well-suited for high-efficiency solar cells without the need for additional high-temperature processing.

This work is a long-term, interannual, and experimental study conducted in multiple locations. It studies the effects of phase change materials (PCMs) on photovoltaic modules’ performance by reducing their operational temperature. Two PV modules were manufactured so that PCM slabs could be mechanically attached to their backside, ensuring contact with the related photovoltaic active area. Experiments were conducted in Delft, Netherlands, from 2019 until 2021 and in Catania, Italy, during the winter and start of spring of 2023. The experiment also considered two installation layouts: building integrated (Delft) and standard rack-mounted (Catania). The measurements showed that the PCM provides significant cooling under both locations, with a temperature reduction of up to 15 °C. In Delft, thermal control could be obtained for most of the sunny hours of the day, even during the summer months. In Catania, the module with PCM presented, on occasion, higher temperatures than its standard counterpart, primarily due to winter-time environmental conditions. However, the PCM provided sufficient thermal control on all conditions, ensuring increased energy yield. This increase ranged from 2.1 to 2.5 % in Delft and 1.3–1.6 % in Italy.

Enhancement of thermophysical properties of molten salt-based nanofluids is essential to reduce the geometric size and increase the energetic-exergetic efficiency of the thermal energy storage system. Moreover, the thermophysical properties of nanoparticles dispersed molten salt remain unclear, especially the anomalous enhancement of specific heat capacity (Cp). In the present study, the different concentrations (0.5, 1.0 and 2.0 wt%) of silicon carbide nanoparticles (SiC-NPs) dispersed solar salt (i.e., SiC nanosalt) were prepared using the wet chemical method, and their thermophysical properties were evaluated using various differential techniques. The crystalline structure of the SiC-NPs was analysed and confirmed using an X-ray diffractometer (XRD). Further, the size (diameter = 30.61 nm) and shape were identified in the transmission electron microscope (TEM). The differential scanning calorimetry (DSC) analysis was carried out for the prepared SiC nanosalt and found the average specific heat capacity enhancement for 1.0 wt% SiC nanosalt is 14.4 % and 8.1 % in solid (50 °C–200 °C), and liquid (250 °C–350 °C) phases, which is 8.7 % and 3.3 % higher than 0.5 wt% and 2.0 wt%. Further, the scanning electron microscope (SEM) technique was conducted for different wt% of SiC and found random dispersion (for 0.5 wt%), better dispersion (for 1.0 wt%), and agglomeration (for 2.0 wt%). From the combined result of DSC and SEM, the optimal weight loading of SiC-NPs was identified as 1.0 wt%. The thermal conductivity was measured for the prepared sample, and it was found that a thermal conductivity of 2.0 wt% is 8.85 % higher than solar salt. Finally, the thermal stability of the nanosalt was tested in thermogravimetric analysis (TGA), and it found that the maximum weight presence for the maximum wt% of SiC is 92.8 %, which resulted in the weight loss of the SiC nanosalt is similar to solar salt.

The thermal stability of methylammonium lead iodide (MAPbI₃)-based flexible perovskite solar cell (PSC) modules was studied. For this purpose, PSC modules, consisting of 10 serially connected cells with an aperture area of 9 cm², were heated at 85 °C, 95 °C, and 105 °C for 4000 h. The solar cell parameters were periodically measured by interrupting the thermal stability tests. Evolution of series resistance, short circuit current, and fill factor showed monotonic reduction, whereas shunt resistance and open circuit voltage depicted three stage degradation: (i) initial rapid degradation; (ii) quasi stable range; and (iii) gradual monotonic degradation stages, which are the indication for the presence of several degradation mechanisms. Using the Arrhenius model, activation energy (E_a) of degradation was studied. E_a of 1.062 eV (102.5 kJ/mol) was obtained for the maximum output of the total device. Device lifetime for thermal stability, which is defined as the point where the efficiency has reduced to 80 % of its initial value, was also estimated at module temperature of 45 °C.

In recent years, the research on silicon heterojunction (HJT) solar cells based on dopant-free contacts has experienced rapid development. Zn(O,S) is a low work function n-type semiconductor compound with tunable band gap that can be used as the electron transport layer (ETL) in HJT solar cells. In our work, we choose Zn(O,S) as ETL and deposit it via the low-cost chemical bath deposition (CBD) method. Uniform and fast growth of Zn(O,S) films can be obtained by regulating the concentration of the complexing agent and the ratio of reactants to reduce the generation of impurities. To further achieve band matching with c-Si, the Zn(O,S) films are processed with air-annealing to modify the elemental ratios. The air-annealing lowers the interfacial electron transport barrier, which promotes charge separation and transport, thus reducing carrier recombination at the interface. Finally, the PCE of HJT solar cell based on CBD-Zn(O,S) ETL is close to 15 %, providing a new potential route for the development of low-cost HJT solar cells.

Photothermal functional phase change materials (PCMs) have attracted considerable attention due to their large energy density, which can solve the inherent imbalance defects of solar energy. However, the efficiency determination of the PCM-based photothermal utilization process (including photon absorption, photothermal conversion, thermal storage, and thermal release) is still unclear, especially with different or even contradictory quantitative indexes for the same process, resulting in inaccurate photothermal utilization performance and unfair comparison in various efforts. Herein, we clarified the photothermal utilization sub-processes of phase change composites via optical characterizations and photothermal conversion experiments and highlighted the energy dissipation mechanism of photothermal conversion process by fluorescence and femtosecond transient absorption examination. Besides, the energy flow features of these sub-processes were explored by determining the energy flow and optical/thermal losses. More importantly, we standardized the efficiency of the four sub-processes by proposing evaluation indexes and established the relationship among the four sub-processes to derive the total photothermal utilization efficiency. This work provides a paradigm for a comprehensive investigation of PCM-based photothermal utilization systems, especially establishing consistent criteria for subsequent efficiency determination, laying a solid foundation for developing and quantifying solar thermal utilization systems.

Tunnel oxide passivated contact (TOPCon) crystalline silicon (c-Si) solar cells have attracted much attention because of their superior electrical properties such as the lower contact resistivity and better interface passivation at high temperatures. However, the TOPCon c-Si solar cells also have room for further improvement in optical performance, and the embodiment of optical advantages needs to be matched synchronously in electrical aspect. Here, the rear silicon pyramids with different angles have been achieved through solution corrosion to maximize the light absorption in the c-Si substrate. The light absorption for the pyramid angle of less than 30° is better. Compared with the cell samples with rear pyramid for a certain angle, the samples with flat back surface possess better surface passivation, and the contact resistivity can be reduced effectively by increasing the phosphorus doping concentration and adjusting the annealing temperature. Furthermore, the TOPCon c-Si solar cells with flat rear surface covered by 70 nm poly-Si have been demonstrated to increase the conversion efficiency by about 0.15 % vs. the counterpart for poly-Si of 130 nm thickness, and the improvement is mainly due to the increase of J_SC and FF by 0.07 mA/cm² and 0.72 %, respectively.

The application of nanofluid spectral splitting technology in photovoltaic/thermal (PV/T) systems has attracted more attention. In this study, zinc oxide and silica nanoparticles were selected to prepare ZnO-SiO₂-H₂O mixed nanofluids with different concentrations to investigate the radiative characteristics and their effect on PV/T system. An experimental system was established to measure nanofluids transmission properties in 0.36–2.5 μm, and the radiation characteristics were further analyzed using Mie scattering theoretical model. Besides, thermodynamic model was established to investigate the influence of mixed nanofluids on PV/T system performance. Results indicate that Mie theory can predict the radiative properties of mixed nanofluids well. The ZnO-SiO₂-H₂O nanofluids have better filtering performance than that of ZnO-H₂O nanofluids under same particle concentration. When the mass ratio of ZnO/SiO₂ is 0.01 %/0.05 %, the filtering efficiency of the nanofluid achieves 46.18 %. Increasing the concentration of SiO₂ can regulate the transmittance of the ZnO-SiO₂-H₂O nanofluids and improve the PV/T system efficiency by 5 %. Based on ZnO nanofluids, the addition of SiO₂ further optimizes PV/T system performance, increasing the system merit function (MF) value The nanofluid spectral splitting PV/T system for Si cells with a ZnO/SiO₂ mass ratio of 0.003 %/0.056 % can reach a MF value of 1.342.