Low-conductivity doped layers for improved performance of thin film silicon solar cells on highly textured substrate
The performances of thin film silicon solar cells are reported for the use of increasingly rough zinc-oxide (ZnO) front electrodes. Experimental results show that textured substrates favor increased light trapping but also the local creation of undesired current drains, degrading the electrical performance of the cells. While an appropriate plasma treatment of the ZnO surface and a high silicon material quality are required to decrease the density of such current drains, doped nano-crystalline silicon oxide layers are proposed to limit the impact of these local non-uniformities onto the performance of both hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) junctions. The possible physical roles of such low-conductivity doped layers are discussed. Conversion efficiency relative increase of 7 % for a-Si:H single junction and of 4 % to 20 % for respectively low (0.3 nm/s) and high deposition rate (1 nm/s) i-layer in μc-Si:H junctions deposited on highly textured substrates are shown. Micromorph solar cells integrating such doped silicon oxide layers could be developed on rough ZnO front electrodes with a high light trapping potential with up to 13.7 % and 11.5 % initial and stabilized efficiency, respectively.