All Solution-Processed Cu2ZnSnS4 Solar Cell by Using High-Boiling-Point Solvent Treated Ball-Milling Process with Efficiency Exceeding 6%

To improve the crystallinity and overall film quality of the light absorbing layer is vital to further enhance the performance of sulfide Kesterite Cu2ZnSnS4 (CZTS) solar cells, especially for all solution-processed devices using ball-milling processed CZTS that generally leads to poor crystallization. In this work, a novel treatment method involving high-boiling-point solvent (HBPS), via simply spinning oleic acid (OA) solution onto CZTS precursor film coupled with an elongated annealing duration, was for the first time reported that enabled not only reduced surface roughness, but considerably increased crystalline of CZTS film. This is corroborated by an enhanced XRD intensity by eight -fold in conjunction with a five-fold increased steady-state PL intensity, the latter of which also indicates an improved CdZnS/CZTS heterojunction quality. Combined with all solution-processed buffer layer and contact material, device using HBPS-treated ball-milling processed CZTS absorber yielded a power conversion efficiency of 6.1%, which is the highest reported for all solution-processed pure-sulfide CZTS solar cells. The HBPS-treatment approach developed in this work is simple and effective, and in principle can promisingly be applied to any film to work synergistically with thermal annealing treatment, leading to simultaneously enhanced crystallinity and overall film quality while maintaining its planeness.