Dual Functional Dopant-Free Contacts with Titanium Protecting Layer: Boosting Stability while Balancing Electron Transport and Recombination Losses

Combining electron- and hole-selective materials in one crystalline silicon (Si) solar cell, thereby avoiding any dopants, is not considered for application to photovoltaic industry until only comparable efficiency and stable performance are achievable. Here, it is demonstrated how a conventionally unstable electron-selective contact (ESC) is optimized with huge boost in stability as well as improved electron transport. With the introduction of a Ti thin film between a-Si:H(i)/LiF and Al electrode, high-level passivation (S-eff = 4.6 cm s(-1)) from a-Si:H(i) and preferential band alignment (rho(C) = 7.9 m omega cm(2)) from low work function stack of LiF/Ti/Al are both stably retained in the newly constructed n-Si/a-Si:H(i)/LiF/Ti/Al ESC. A detailed interfacial elements analysis reveals that the efficiently blocked inward diffusion of Al from electrode by the Ti protecting layer balances transport and recombination losses in general. This excellent electron-selective properties in combination with large process tolerance that enable remarkable device performance, particularly high efficiencies of 22.12% and 23.61%, respectively, are successfully approached by heterojunction solar cells with dopant-free ESC and dopant-free contacts for both polarities.

Automated summary

This study demonstrates a new approach that combines electron- and hole-selective materials in one crystalline silicon solar cell. By optimizing the stability and electron transport of the electron-selective contact (ESC), high efficiency and stable performance are achieved. The introduction of a thin film in the ESC allows for high-level passivation and preferential band alignment, leading to remarkable device performance.