Study on the improvement of the open-circuit voltage of NiOx/Si heterojunction solar cell

Heterojunction solar cell based on nickel oxide (NiOx) as hole selective layer and n-type silicon as an active absorption layer is a promising high-efficiency solar cell. Unfortunately, this type of solar cells suffers from a low open circuit voltage (VOC) which limits any significant progress in its performance. Therefore, the main scope of this study is focused on VOC improvement. Discrete traps at the NiOx/Si interface are taken into account in the simulation to describe the real situation. The simulation was performed by SILVACO-Atlas using the interfacial traps NiOx/Si concentrations and hole mobility as tools to obtain agreement with measurement reported by Hsu et al. in [Thin Solid Films. 573 (2014) 159–163]. These parameters were found to be the cause of the low VOC value. VOC and efficiency improvements were achieved by optimizing the NiOx thickness and insertion a hydrogenated amorphous Si (a-Si:H) thin layer with optimal properties (electron affinity, bandgap and thickness)as a buffer layer between NiOx and Si. VOC increased from 423 to 906.16 mV and a good promising efficiency of η=12.73% is obtained in comparison to the initial efficiency (4.50%). •NiOx/Si heterojunction solar cell suffers from a low open circuit voltage.•This study focuses on finding the reason of low open circuit voltage.•A good agreement with the measured values was achieved.•An amorphous hydrogenated silicon buffer layer is inserted and optimized.