Enhancing Grain Growth for Efficient Solution-Processed (Cu,Ag)2ZnSn(S,Se)4 Solar Cells Based on Acetate Precursor.

Material crystallinity is the overriding factor in the determination of the photoelectric properties of absorber materials and the overall performance of photovoltaic device. Nevertheless, in Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic device the bilayer or tri-layer structure for the absorber have been broadly observed, which are generally harmful to the cell performance due to the probability of photogenerated carrier recombination at grain boundaries significantly increased. Herein, our experiment reveals that application of anions to a new family of (Cu,Ag)2ZnSn(S,Se)4 (CAZTSSe) materials leads to the increase of grain size and crystallinity. It is inspiring that by using acetate starting materials in precursor solution, a uniform, compact and pinhole-free CAZTS precursor film was obtained, and the smoothness of the films surpassed that of films fabricated from oxide route. More importantly, the crystallization of the CAZTSSe film has been considerably enhanced after selenization, large grains go through the entire absorber layer was successfully obtained. Additionally, it is observed that the Voc accompanied by excellent crystallinity improved significantly due to the pronouncedly reduced carrier recombination loss at grain boundaries. As a consequence, the power conversion efficiency (PCE) of the CAZTSSe photovoltaic device is successfully increased from 10.35% (oxide route) to 11.32% (acetate route). Importantly, our work attest to the feasibility of tuning the crystallization of the CZTSSe film by simple chemistry.