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The lateral transport of minority carriers in the surface inversion layer of a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was experimentally analyzed to study defects/traps at the aSi:H/cSi interface and/or on the cSi surface. To extract the lateral surface inversion layer current, a field-effect transistor type test element group device was designed and fabricated on a cSi wafer where SHJ cells were co-integrated. By analyzing the lateral surface inversion layer current, the effective surface minority carrier mobility was calculated. The extracted mobility was one order of magnitude smaller than that of a reference MoOx/i-aSi:H/cSi structure but it increased by low-temperature post-deposition annealing with respect to the reference. This method is highly sensitive to the quality of the aSi:H/cSi interface and/or the cSi surface. The density of trap sites was estimated to be of the order of 1011 cm−2 at the aSi:H/cSi interface and/or on the cSi surface. [ABSTRACT FROM AUTHOR]

We investigated the effect of silicon dioxide (SiO2) film in n-type front-emitter (n-FE) crystalline Si solar cells on the potential-induced degradation (PID) of n-FE photovoltaic modules. After PID tests by applying a bias of −1000 V at 85 °C for a few min, the modules with the cells without SiO2 did not degrade in the short-circuit current density and the open-circuit voltage (Voc). Since the degradation is known to be due to positive charge accumulation in SiNx films, the result suggests that such SiO2 acts as barriers to retain accumulated positive charges. After further PID tests, modules without SiO2 show faster and more significant degradation by a decreases in the fill factor (FF) and the Voc. It has been proposed that the degradation in the FF and Voc is caused by sodium (Na) introduction into cells. The results therefore suggest that SiO2 delays Na migration. [ABSTRACT FROM AUTHOR]

It was experimentally found that surface recombination due to charge accumulation, called polarization-type potential-induced degradation (PID), occurs by applying high voltage in n-type crystalline Si photovoltaic (PV) modules. By contrast, polarization-type PID has not been observed yet in p-type crystalline Si PV modules. We investigated the effect of differences in anti-reflection coating (ARC) and the conduction type of the substrate used as a base for PV cells on PID. PID was examined for PV modules using p-type and n-type crystalline Si PV cells with a SiNx or SiNx/SiO2 stacked ARC layer. The results indicate that PID owing to charge accumulation occurs even for p-type crystalline Si PV modules by applying high positive voltage. Furthermore, we found that polarization-type PID due to charge accumulation in ARC, leading to surface recombination, is due not to the conduction type of the substrate but to the ARC structure. [ABSTRACT FROM AUTHOR]

In this study, we investigated progression of potential-induced degradation (PID) in photovoltaic modules fabricated from n-type-based crystalline-silicon cells with front p+ emitters. In PID tests in which a bias of −1000 V was applied to the modules, they started to degrade within 5 s and their degradation saturated within 60 s. This behavior suggested that the PID was caused by positive charge accumulation in the front passivation films. Performing PID tests with a bias of −1500 V revealed that the degradation rate strongly depended on the applied bias whereas the saturation value was independent of the applied bias. Regeneration tests on degraded modules previously subjected to PID tests for durations of 5 and 10 min were performed by applying a positive bias of +1000 V. All the degraded modules completely recovered their performance losses within 60 s regardless of the degradation test duration. On the basis of these results, we proposed that these positive charges originate from positively charged K centers formed by extracting electrons from neutral and negatively charged K centers. This model readily explains the observed degradation and regeneration behavior. To test our model, we determined the fixed positive charge densities (Qf) of a silicon nitride passivation film before and after PID, for which it was found that Qf showed similar saturation behavior. Additionally, the saturated Qf value was of the same order as K center density. These results support our model involving a charging process of K centers. [ABSTRACT FROM AUTHOR]

We report on our attempt to increase the carrier density in the p-type polycrystalline silicon (poly-Si) layers grown by aluminum-induced crystallization (AIC) employing a B-doped Si target. Hall measurement revealed that we could obtain a lower-resistance and heavily doped p-type continuous poly-Si thin layer formed by AIC using B-doped a-Si. According to our evaluation of tunnel oxide passivated contact (TOPCon) solar cells with AIC-grown poly-Si, the AIC-TOPCon solar cells fabricated at 570 °C using B-doped a-Si showed higher conversion efficiency of 13.5% than that of 12.8% when using nondoped a-Si. It is considered that the cell characteristics, particularly FF and Voc, were improved owing to the lower series resistance and higher carrier density since both Al and B were successfully incorporated into the AIC-grown poly-Si. [ABSTRACT FROM AUTHOR]

Si ingots were sliced using a diamond-coated wire, and saw damage was observed even after damage removal etching and texturization. Since invisible microscopic damage was observed only under uncontrolled slice conditions, such damage was identified as saw damage. The wafers with saw damage exhibited the degradation of solar cell conversion efficiency (approximately 1–2% absolute). The results of external quantum efficiency (EQE) measurements showed a slight deterioration of EQE in the short wavelength region. Current–voltage characteristic measurements showed similar results that agreed with the EQE measurement results. In addition, EQE mapping measurements were carried out at various irradiation wavelengths between 350 and 1150 nm. Areas with dark contrasts in EQE mapping correspond to saw damage. In the cells with a low conversion efficiency, both EQE mapping and PL images exhibited dark areas and lines. On the other hand, in the cells with a high conversion efficiency, a uniform distribution of saw damage was observed even with the saw damage in the PL images. We believe that sophisticated control to suppress saw damage during sawing is required to realize higher conversion efficiency solar cells in the future. [ABSTRACT FROM AUTHOR]

We have grown 50 cm2 mono Si ingots by the seed cast technique. The carbon and oxygen concentrations of the ingots have been significantly reduced by improving the gas flow condition and coating. The dislocation density was also reduced by eliminating the extra dislocation generation sources. Owing to these developments, the lifetime of wafers has reached 465 µs. Finally, the efficiency of 18.7% has been achieved, which is comparable to 18.9% of the reference Czochralski (CZ) Si wafer. [ABSTRACT FROM AUTHOR]