Progress in Photovoltaics最新文献

Large-scale daylight photoluminescence imaging of crystalline silicon solar panels in utility-scale solar farms, whereby luminescence images of several hundred to thousands of panels are acquired simultaneously, was demonstrated by our group recently. Here, we demonstrate that photoluminescence images of large solar farm sections that are connected to the same central inverter uniquely contain quantitative information about voltage mismatch between series-connected strings of modules resulting from voltage variations between groups of modules. These voltage variations cause significant balancing currents between module strings when no or only low power is extracted from the solar farm. The impact of these balancing currents on the luminescence intensity is discussed. An analytical model to correct daylight photoluminescence images for these balancing currents is proposed and validated using experimental data.

The advantage of employing an n-type hydrogenated nanocrystalline silicon oxide (nc-SiO_x:H) layer as the front surface field (FSF) in silicon heterojunction (SHJ) solar cells is due to its low optical absorption coefficient and tunable refractive index. However, carbon dioxide (CO₂) gas, one of the major precursor gases in the nc-SiO_x:H layer, deteriorates the crystallinity, which is one of the key factors affecting cell performance. Here, we successfully deposited a nc-SiO_x:H FSF layer with high crystallinity for SHJ solar cells by using nitrous oxide (N₂O) as an alternative oxygen source instead of existing CO₂. Compared with the use of CO₂, the use of N₂O as an oxygen source can achieve a 10% ~ 15% increase in the deposition rate of the nc-SiO_x:H layer, which can shorten the total processing tact-time, thus having the potential to reduce production costs in large-scale industrial applications. The influence of N₂O as an oxygen source on the film properties was also investigated. By optimizing the proportion of N₂O in the precursor gases, we finally fabricated 274.5 cm²-area SHJ solar cells with an in-house average efficiency of 25.76%, which is approximately 0.1%_abs higher than that of their reference counterparts (using CO₂ as an oxygen source), and obtained a certified efficiency of 25.79% for the champion cell independently confirmed by the ISFH CalTeC in Germany.

A simple binary antimony selenide (Sb₂Se₃) absorber is evolving as an alternative photovoltaic material in thin film solar cells because of its unique properties and easy processing. Sb₂Se₃ thin films having good crystalline quality are grown via versatile thermal evaporation from pre-synthesized near stoichiometric compound material on molybdenum-coated soda lime glass (SLG) and borosilicate glass (BG) substrates. Following the systematic characterizations on the absorber films, substrate configured Sb₂Se₃/CdS heterojunction devices were fabricated and their photovoltaic characteristics have been studied using current density vs. voltage (J-V), dark J-V modeling, external quantum efficiency and capacitance vs. voltage measurements. The power conservation efficiency values of 4.88% and 5.04% were achieved for the devices fabricated on SLG and BG substrates, respectively with deficit in open circuit voltage. The obtained values are higher in comparison to the reported device efficiencies in substrate configured Sb₂Se₃ solar cells, in which the absorber is prepared through thermal evaporation. To understand the loss in open circuit voltage_, a compact equivalent circuit model was considered and identified the contribution of different shunt leakage paths in the devices. In addition to that, the device fabricated on the SLG was stable with minimal changes in its photovoltaic performance for a period spanning over 200 days. The results obtained are encouraging with scope for improving the device performance through interface engineering and back surface passivation strategies.

TOPCon solar cell with boron (B)-doped emitters plays an important role in photovoltaic cell technology. However, a major challenge to further improving the metallization-induced recombination and electrical contact of B-doped emitters. Laser-enhanced contact optimization (LECO) technology is one of ideal candidates for reducing the metallization recombination and contact resistivity. In this study, we investigate the influence of LECO technology using special Ag paste with a decreased Pb content on the performance of the metallization-induced recombination (J₀,_metal), contact resistivity (ρ_c), microtopography of the contact, the I–V parameters, and possible conductive mechanisms. The results showed that the linear resistivity is reduced from 3.56 to 2.60 μΩ·cm owing to special Ag paste, and after LECO treatment, it also has lower ρ_c about 0.91 mohm·cm². Both of them have a large contribution to the FF enhancement. Meanwhile, the J_0,metal drops from 500 to 200 fA/cm², which provides a great contribution to the improvement in open-circuit voltage. The efficiency improved by 0.26% absolute to 25.94%, mainly because of the increased open-circuit voltage (V_oc) of 4 mV and a fill factor (FF) of 0.26%. Simulated by COMSOL, the electron concentration rises to 4 × 10¹⁹ cm⁻³ after LECO treatment, which can generate a larger reverse current to provide a melting temperature for the glass frit, increasing the interface glass phase conductivity. The possible current transport mechanism of LECO is current tunneling effect, resulting in the decrease in the metallization recombination. After the optimization of the LECO process with low-corrosion paste, we manufactured industrial-grade TOPCon cells with E_ff, V_oc, J_sc, and FF values as high as 26.5%, 736 mV, 42.1 mA/cm², and 85.5%, respectively.

Flexible, lightweight thin film (TF) photovoltaic (PV) modules offer a unique opportunity for integration into non-planar surfaces unable to support heavy weights. While such applications increase the potential for PV in urban areas, the reliability implications are yet to be investigated. Here, prototypes of corrugated rooftiles with integrated Cu (In,Ga)Se₂ (CIGS) modules were investigated after 3 years of outdoor operation. Their performance before and after the outdoor exposure was compared and defects were localized. An unpackaging method was developed, allowing access to the solar cells for more detailed characterization of present defects without causing additional damage or changes to existing defects. To our knowledge, this was the first time such an unpackaging method was successfully applied to flexible TF PV modules. The relative efficiency loss ranged from 17% to 43%, mostly due to short-circuit current (I_SC) loss and series resistance (R_S) increase. The predominant cause of the R_S increase was the delamination at the interconnects, ascribed to thermomechanical stresses caused by outdoor temperature fluctuations. The I_SC loss was mainly caused by localized delamination of CIGS from the molybdenum (Mo) back-contact. The occurrence of such delaminated areas pointed to presence of high local stresses during outdoor operation, possibly due to thermal fluctuations, applied deformation and/or mechanical impact. Two other types of delamination defects were found with no observable impact on performance. These results show the necessity for further optimization in the material choice and processing of TF flexible modules, to avoid mechanical stress related failures upon integration into curved surfaces.