J-V Distortion of CIGS Solar Cells with Sputtered Zn(O,S) Buffer Layer*

Sputtered-deposited Zn(O,S) is an attractive alternative to CdS for Cu(In,Ga)Se2 (CIGS) thin-film solar cells' buffer layer. It has a wider band gap and thus allows greater blue photon collection to achieve higher photon current. A key parameter for the sputtering deposition of Zn(O,S) has been the oxygen fraction in the argon sputtering beam. Current-Voltage (J-V) distortion, observed in some cases, varied with oxygen fraction in Zn(O,S). The details are in good agreement with predictions of a photodiode model, in which a conduction-band offset (CBO)-induced barrier at the buffer-absorber interface is responsible for the distortions (both red kink and crossover). Varying oxygen fraction in Zn(O,S) may play a role in adjusting the CBO at the interface and thus modulating the J-V distortion.