Chalcogenide solar cells fabricated by co-sputtering of quaternary CuIn0.75Ga0.25Se2 and In targets: Another promising sputtering route for mass production

Abstract

In this work, Cu(In1−xGax)Se2 (CIGS) absorber layer is fabricated via radio-frequency sputtering of standard quaternary CuIn0.75Ga0.25Se2 target. In order to achieve the desired Cu-poor absorber film stoichiometry, which is crucial for the device performance, indium is supplied simultaneously with the CIGS deposition by direct current sputtering of indium target for the first time. The influences of sputtering power on composition, structure of the CIGS absorber films and the performances of related solar cells are systematically investigated. The precursor absorber film exhibits uniform and compact surface morphology without peeling and cracking. After selenized in a tube-type rapid thermal processing system under a Se atmosphere, the CIGS absorber layer possesses columnar grains with preferred (112) orientation. Photoelectric measurements of the most efficient device with CdS buffer and ZnO window layer reveals a short-circuit current of 32.02 mA/cm2, an open-circuit voltage of 532 mV, and a fill factor of 60.5 under standard conditions. The efficiency of up to 10.29% on 0.35 cm2 area without antireflection coating has been achieved. Our new sputtering route shows great potential for practical applications of thin film CIGS solar cells with in-line sputtering processes.