Characterisation of direct epitaxial silicon thin film solar cells on a low-cost substrate

Direct epitaxial crystalline silicon thin film (CSiTF) solar cells on low-cost silicon sheets from powder (SSP) ribbons have been prepared using rapid thermal chemical vapour deposition (CVD) growth. The characterisation of CSiTF solar cells was investigated by electron and spectrally resolved light beam induced current (EBIC and SR-LBIC, respectively). All EBIC measurements were performed on both the front-side surface as well as on the cross-section of CSiTF solar cells. The electrical recombination was detected by EBIC and compared with their morphologies. The results of EBIC scan show that recombination centres are situated at grain boundaries (GBs); higher the density of grain, higher the recombination activities (higher contrast). Recombination of different intensity (strong and weak) takes place at vertical GBs. Compared with the high recombination at GBs, the contrast in intragrain is low. The dark contrast of the GBs and intragrain defects is clearly reduced near the surface due to the passivation by hydrogen, which indicates that the minority carrier diffusion length decreases gradually with the depth perpendicular to the surface. The diffusion length was determined by SR-LBIC. The results show that the diffusion length distribution is quite inhomogeneous over the whole cell area. A maximum Leff of about 25 μm and mean values around 15 μm are calculated for the best solar cell.