Efficient separation and collection of photogenerated carriers through the formation of asymmetric electron and hole transport channels is one of the key issues for crystalline silicon (c-Si) solar cells and other types of photovoltaic devices.

Silicon heterojunction solar cells based on MoO_x (x<3) hole-selective contacts show significant advantages in carrier-selective transport. However, they face the challenge of long-term stability due to poor thermodynamic stability of MoO_x. 

A research team led by Prof. LI Dongdong at the Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences and their collaborators reported a novel stacked structure to improve the stability of c-Si solar cells.

The study was published in Advanced Functional Materials on August 26.

The research team introduced a SiO₂ tunneling passivation layer at the MoO_x/c-Si interface to suppress the redox reaction caused by the direct contact between MoO_x and c-Si, which keeps the work function of MoO_x at a relatively high level.

An ultra-thin V₂O_x layer was deposited on the surface of MoO_x film to improve the stability of the heterojunction structure in air and its resistance to sputtering damage.

At the same time, the indium tin oxide (ITO) layer was fabricated at the V₂O_x/Ag interface, which effectively inhibited the migration of metal ion, and finally constructed a tandem structure of c-Si/SiO_x/MoO_x/V₂O_x/ITO/Ag, with power conversion efficiency (PCE) of 20.0% and improved stability. 

This work solved the stability issue of p-Type silicon solar cells with full area Si/ MoO_x/Ag contacts by introducing stable oxide layers on both sides of MoO_x to prevent the interfacial reaction and evolution.

It provides a new approach to the study of compound/c-Si passivated contact heterojunction solar cells, which can be extended as a universal method to improve the efficiency and stability of heterojunction solar cells and other types of optoelectronics. 

The study was supported by the National Natural Science Foundation of China, the Natural Science Foundation of Shanghai, the Shanxi Science and Technology Department, and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.