Numerical investigation of energy level strategy for TMO/Si tunneling heterojunction solar cells

A thin film of transition metal oxide (TMO) layer forms a heterojunction configuration with silicon (Si) via dopant-free fabrication process. However, excellent hole selective contact performance of TMO/n-Si heterojunction necessitates a stringent alignment of energy levels. Herein, we studied the level matching strategy of TMO/n-Si heterojunction with four parameters including conduction band (E_C), bandgap (E_g), Fermi level (E_F) and interface trap concentration (N_t). It is found that the electron affinity (E_a) of TMO determines the relative position of the energy level, and increasing the E_a can increase the open-circuit voltage (V_OC) from 426.0 to 742.5 mV. In addition, the energy level bending of the interface can be adjusted by the relative E_F position of TMO and n-Si to improve the carrier separation efficiency to increase the short-circuit current density (J_SC). Meanwhile, the higher N_t is beneficial to the carrier tunneling transport in the case of E_C of TMO being smaller than that of n-Si, which enhances the energy level bending of the interface and improves the solar cells performance. Finally, the MoO_x/n-Si heterojunction solar cell is optimized to obtained the power conversion efficiency (PCE) of 21.87%.