Effects of CuAlO2 on the heterojunction interface and performance of Cu2ZnSn(S,Se)4 thin-film solar cells

Carrier transportation and efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are seriously inhibited due to heterojunction interface (HEI) recombination. Herein, we firstly propose a novel HEI doping strategy to address HEI recombination issue by introducing Cu-poor (& Al-rich) CuAlO2 (CAO). Our results indicate that interfacial elements interdiffusion took place between Cu from absorber and Al from CAO during selenization. Then, occupation of Al on the Cu site leads to the absorber shallow bulk inversion from p to n-type, and thereout constructs a desirable homogeneous field passivation (HFP) for HEI. It has not only a superior photo-induced charge carrier transportation function and penalizes the probability of electron-hole recombination but also leads to the superior carrier separation capacity via enlarging depletion region. In addition, CAO itself can bring about a chemical passivation effect owing to its high resistivity. As a result, synergistic passivation effect combining common chemical passivation with novel HFP was realized. Finally, we achieved 9.34% efficiency kesterite device involving chemical and field passivation effects simultaneously despite the relatively not top efficiency. In this regard, HEI doping engineering induced with characteristic Cu-poor (& Al-rich) material for absorber shallow bulk inversion and appreciable passivation effect achieved here shine a new light on the development of kesterite device.