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%.