Structures of Cu(In,Ga)(S,Se)2 solar cells for minimizing open‐circuit voltage deficit: Investigation of carrier recombination rates

Cu(In,Ga)(S,Se)2 (CIGSSe) solar cell structures are designed to reduce open‐circuit voltage deficit (VOC,def) for the enhancement of power conversion efficiency (η) through the optimizations of conduction band offsets not only between the buffer and absorber (ΔEC‐BA) but also between the transparent conductive oxide and absorber (ΔEC‐TA). Voltage‐independent carrier recombination rates at buffer/absorber interface (Ri0), in space‐charge region (Rd0), and in quasi‐neutral region (Rb0) of the CIGSSe solar cells with different structures are separately extracted. Consequently, the development of device structures with similar CIGSSe quality leads to the primary reduction of Ri0, while Rd0 and Rb0 are not varied very much, thus minimizing the VOC,def. It is disclosed that the solar cell structure of CIGSSe/Cd0.75Zn0.25S/Zn0.8Mg0.2O/Zn0.9Mg0.1O:Al together with K‐treated CIGSSe absorber is appropriate with the ΔEC‐BA of 0.31 eV and ΔEC‐TA of 0.37 eV, thereby significantly decreasing Ri0 and VOC,def to approximately 1.1 × 104 cm−2 s−1 and 0.374 V, respectively, and increasing the η to 21.1%. Structure development leads to decreases in voltage‐independent carrier recombination rate at buffer/absorber interface (Ri0) and open‐circuit voltage deficit (VOC,def) through optimizations of conduction band offsets between buffer and absorber and between transparent conductive oxide and absorber. K‐treated Cu(In,Ga)(S,Se)2 absorber yields further decreases in Ri0 and VOC,def, enhancing conversion efficiency to 21.1%.