Cu gradient design to attain high efficient solution-processed CuIn(S,Se)2 solar cells

Solution-processed chalcopyrite solar cells are widely regarded as a promising alternative method in reducing the cost compared with vacuum-based techniques. It is noted that the absorber layer usually needs to be prepared under a high insert pressure (∼1.6 atm) to suppress element loss or under a mild pressure but additional surface etching is needed for fabricating high efficient solar cell. Herein, a copper gradient structured precursor is proposed to prepare CuIn(S,Se)₂ (CISSe) film under a mild pressure (1.1 atm). The designed gradient Cu not only promotes crystal grain growth and tailors the defects, but also avoids the surface etching of the formed CISSe film for the fabrication of high efficient solar cells. Further, Cu gradient design decreases the conduction band offset of heterojunction, boosting the carriers transport across the p-n heterojunction. Accordingly, a 13.35% efficient CISSe solar cell, comparable to the high efficient CISSe solar cell prepared by this method under high pressure or with film surface etching, is fabricated. This work provides a facile pathway to fabricate high efficient solution-processed chalcopyrite solar cell, avoiding high selenization pressure and film etching, and shows huge potential for solution-processed copper-based solar cells.