Tailoring protective metals for high-efficient and stable dopant-free crystalline silicon solar cells

Dopant-free passivating contacts have the potential to be deposited at low costs while exhibiting excellent electrical performance for photovoltaic devices. However, one significant issue of such a technology is the unsatisfactory environmental stability compared to the conventional doped-silicon contacts. Herein, we propose a strategy for improving the stability and the electrical properties of typical electron-selective contacts (ESCs) with a i-a-Si:H/LiF/Al stack by inserting thermally evaporated thin metal films as protective layers. Particularly, Yb, Mg, Ti and Ni materials are investigated in detail to address their electrical behaviors, including contact and passivation properties, as well as their stability under annealing treatments. Finally, the Ti-modified ESC exhibited the highest device performance and the best thermal stability, enabling the development of front and back contacted silicon heterojunction solar cells with a remarkable power conversion efficiency (PCE) of 22.14% and maintaining more than 90% of the initial PCE after annealing at 200 degrees C. The protective metal layer deposited by a facile approach offers a surplus of opportunity to develop high-efficient and cost-effective dopant-free crystalline silicon solar cells.