Structural tuning of wide-gap chalcopyrite CuGaSe2 thin films and highly efficient solar cells: differences from narrow-gap Cu(In,Ga)Se2

ABSTRACTSimultaneous realization of high values of open circuit voltage (Voc), fill factor (FF), and energy conversion efficiency (η) in wide‐gap CuGaSe2 (CGS) solar cells has long been one of the most challenging issues in the realm of chalcopyrite photovoltaics. In this communication, structural tuning of CGS thin films by means of controlling the amount of Se flux used during CGS film growth and improvements in solar cell performance (Voc > 0.9 V, FF > 0.7, and η > 10%) are demonstrated. Systematic variations in CGS film properties with the Se flux and correlation with device properties are shown. The unique CGS thin‐film growth kinetics, which are different from narrow‐gap Cu(In,Ga)Se2, are also presented and discussed. This development of double digit efficiency for CGS solar cells opens a new frontier for the broad application of a new class of chalcopyrite‐based devices. Copyright © 2014 John Wiley & Sons, Ltd. Wide‐gap chalcopyrite CuGaSe2 (CGS) thin‐film solar cells can demonstrate high open circuit voltages (>0.9 V) and high fill factors (>0.7) with high energy conversion efficiencies (>10%) by controlling the Se to Ga flux ratio P[Se]/[Ga] during CGS film growth. Variations in CGS film and device properties observed with various P[Se]/[Ga] are dramatically different from In‐containing Cu(In,Ga)Se2.