Effect of light trapping in an amorphous silicon solar cell

• A theoretical analysis of light trapping in p–i–n and n–i–p type solar cells
• Jsc increases and Voc decreases with the increase in i-layer thickness.
• Observed optimized thickness of i-layer as 400 nm
• Jsc improved from 15.4 mA/cm2 to 16.6 mA/cm2 due to the light trapping.
• Efficiency (η) improved from 9.7% to 10.6% due to better red response of the EQE.

Light trapping in amorphous silicon based solar cell has been investigated theoretically. The substrate for these cells can be textured, including pyramidally textured c-Si wafer, to improve capture of incident light. A thin silver layer, deposited on the substrate of an n–i–p cell, ultimately goes at the back of the cell structure and can act a back reflector to improve light trapping. The two physical solar cells we investigated had open circuit voltages (Voc) of 0.87, 0.90 V, short circuit current densities (Jsc) of 14.2, 15.36 mA/cm2 respectively. The first cell was investigated for the effect on its performance while having and not having light trapping scheme (LT), when thickness of the active layer (di) was changed in the range of 100 nm to 800 nm. In both the approaches, for having or not having LT, the short circuit current density increases with di while the Voc and fill factor, decreases steadily. However, maximum cell efficiency can be obtained when di = 400 nm, and hence it was considered optimized thickness of the active layer, that was used for further investigation. With the introduction of light trapping to the second cell, it shows a further enhancement in Jsc and red response of the external quantum efficiency to 16.6 mA/cm2 and by 11.1% respectively. Considering multiple passages of light inside the cell, we obtained an improvement in cell efficiency from 9.7% to 10.6%.