LAUSR

To improve the conversion efficiency of Cu(In,Ga)Se2 (CIGS) solar cells, we clarified the correlation between the recombination at CdS/CIGS interface and donor concentration in a CdS buffer layer, and propose a technique to control the donor concentration in CdS by In doping. A theoretical analysis was performed for CIGS solar cells with Al/ZnO:B/i-ZnO/CdS/CIGS structure. Open-circuit voltage and fill factor increased with CdS donor concentration. Increasing the CdS donor concentration, the hole-carrier density at the CdS/CIGS interface decreases, leading to the suppression of interfacial recombination. To verify the In-doping effect, CdS films covered with a thin In2 S3 layer were evaluated after an air-annealing process. Carrier concentration increased from 2.4 × 10 15 cm−3 in nonannealed CdS films to 1.1 × 1016 cm−3 in In-doped CdS films with air annealing at 150 °C, indicating that In doping is useful to control the donor concentration in CdS. Finally, In-doping treatment was applied on the CdS buffer layer of CIGS solar cells. Using the nonannealed CdS, efficiency was 15.7%, whereas 17.0% was obtained with the In-doped CdS, which represents an absolute gain of 1.6%. These results indicate that the control of donor concentration in the CdS buffer layer contributes to the reduction of CdS/CIGS interfacial recombination and improves the CIGS solar cells efficiency.