Towards higher efficiencies for crystalline silicon solar cells using SiC layers

Abstract

We investigate the surface passivation potential of SiC on symmetrical lifetime samples and on cell level. To investigate the influence of the deposition conditions on the passivation quality, lifetime measurements on symmetrical samples using the QSSPC technique were performed. The symmetrical lifetime samples were fired to simulate the fire through process used in a standard screen printed solar cell process. Maximum effective lifetime measured on n-type substrate was 3.7 ms at CH4/SiH4=1. Firing of the samples led to a drop in effective lifetimes of about one decade. Maximum effective lifetime after firing was 148 μs at CH4/SiH4=6. To avoid losses in passivation quality caused by the firing step, a buried contact solar cell process was chosen. As cell metallization is done via electroless plating in this process, no firing step is necessary. Rear contacts were realized by laser fired contacts. Reference cells were processed with full area Al-BSF. Fillfactors were reduced because of front side metallization problems. IQE in the long wavelength regime is significantly higher for the SiC passivated cell than for the cell with Al-BSF. Fitting of the IQE data gave rear a SRV of 520-600 cm/s for the cell with SiC passivation and 750-900 cm/s for the cell with Al-BSF.