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 (V-OC,V-def) for the enhancement of power conversion efficiency (eta) through the optimizations of conduction band offsets not only between the buffer and absorber (Delta EC-BA) but also between the transparent conductive oxide and absorber (Delta EC-TA). Voltage-independent carrier recombination rates at buffer/absorber interface (R-0(i)), in space-charge region (R-0(d)), and in quasi-neutral region (R-0(b)) 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 R-0(i), while R-0(d) and R-0(b) are not varied very much, thus minimizing the V-OC,V-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 Delta EC-BA of 0.31 eV and Delta EC-TA of 0.37 eV, thereby significantly decreasing R-0(i) and V-OC,V-def to approximately 1.1 x 10(4) cm(-2) s(-1) and 0.374 V, respectively, and increasing the eta to 21.1%.