Influence of the Frontside Charge Inversion Layer on the Minority Carrier Collection in Backside Contacted Liquid Phase Crystallized Silicon on Glass Solar Cells

Abstract

External quantum efficiency and light beam induced current measurements were used to investigate backside contacted solar cells made on p‐type, liquid phase crystallized silicon on glass (LPC‐Si). Among other differences, these cells had either a SiOxNy or an Al2O3/SiO2 based frontside surface passivation (interlayer). From the measurements it was observed that the cell with the SiOxNy interlayer showed a charge carrier collection from below the absorber contact and from outside the cell area that is much larger than expected from the typical diffusion length in LPC‐Si. This was in contrast to the cell with the Al2O3/SiO2 interlayer, which showed the expected behavior. It was also observed that for the cell with the SiOxNy interlayer, both the collection outside and the collection inside the cell area were strongly bias light dependent. It is argued that these charge carriers collected from outside the cell area are collected through a frontside charge inversion layer. This was supported by an analysis of the measured wavelength and bias light dependence of the collection outside the cell area for the cell with the SiOxNy interlayer. The measured fixed charge density of the interlayer stack with the SiOxNy layer was used to estimate the sheet resistance of the frontside charge inversion layer and this sheet resistance could explain the bias light dependence of the collection outside the cell area. The fixed charge density was also used to simulate the excess carrier density dependence of effective surface recombination at the SiOxNy/c‐Si interface and these simulation results could explain the bias light dependence of the collection inside the cell area.

Passivation of Liquid‐Phase Crystallized Silicon With PECVD‐SiNx and PECVD‐SiNx/SiOx

“…Apart from passivating the buried LPC‐Si surface toward the glass substrate, the ILs need to prevent dewetting of the absorber during crystallization, they have to impede impurity diffusion from the glass into the silicon, and they should enhance light coupling into the absorber when illuminating the cell through the glass side. To meet all these requirements, multi‐layer stacks based on, for example, amorphous silicon oxide (SiO x ), amorphous silicon nitride (SiN x ), amorphous silicon oxynitride (SiO x N y ), amorphous silicon carbide (SiC x ), and aluminum oxide (AlO x ) deposited by using plasma‐enhanced chemical vapor deposition (PECVD), reactive RF‐magnetron sputtering (PVD), or atomic layer deposition (ALD) were successfully integrated into LPC‐Si solar cells.…”