Flexible solar cells with a Cu(In,Ga)Se2 absorber grown by using a Se thermal cracker on a polyimide substrate

A polyimide substrate was used for the fabrication of flexible Cu(In,Ga)Se2 (CIGS) thin-film solar cells. To deposit a stable Mo layer on a flexible substrate, we measured the residual stress in the polyimide film after the deposition of a Mo layer by varying the process pressure. A CIGS absorber was deposited on a Mo layer at a growth temperature below 500℃ by using a Se thermal cracker and various cracking zone temperatures (TC) to improve the reactivity of Se due to the low process temperature. To investigate the effect of Na on the efficiency of a flexible CIGS solar cell, we deposited a Mo:Na layer as a source of Na between the Mo layer and the polyimide substrate. In case of the flexible CIGS solar cell fabricated under the condition of a TC of 800℃ with a Mo:Na layer, the highest cell efficiency was achieved at 10.76% without an anti-reflection coating, which is significantly increased by 4% compared to the efficiency of a solar cell without the Mo:Na layer.