Piezophototronic Effect Enhanced Photoresponse of the Flexible Cu(In,Ga)Se₂ (CIGS) Heterojunction Photodetectors

Abstract The Cu(In,Ga)Se₂ (CIGS) heterojunction, as a mature and high efficiency thin‐film solar cell, is rarely studied as a photodetector, especially in flexible substrates. In this paper, the structure of an ITO/ZnO/CdS/CIGS/Mo heterojunction is grown on the polyimide (PI) substrate to form a flexible CIGS heterojunction photodetector. The photodetector can work in a very wide band ranging from 350 to 1200 nm with responsivity up to 1.18 A W⁻¹ (808 nm), detectivity up to 6.56 × 10¹⁰ Jones (cmHz^1/2 W⁻¹), and response time of 70 (/88) ms, respectively. Moreover, the piezophototronic effect is first used to investigate performance modulation of this device by effectively controlling the separation and transport of carriers at the interface of CdS/ZnO. Interestingly, by externally applying a 0.763% tensile strain, the photoresponsivity and detectivity of the photodetector exhibit a decrease from 1.18 to 0.88 A W⁻¹, and from 6.56 × 10¹⁰ to 4.81 × 10¹⁰ Jones, respectively, while under a –0.749% externally static compressive strain, the photoresponsivity could be enhanced by ≈75.4% with a maximum of 2.07 A W⁻¹, and the detectivity is improved by ≈66.1% with its peak value up to 10.9 × 10¹⁰ Jones. Meanwhile, the response time can be modulated from 99(/116) to 41.3(/42.6) ms. This work suggests that the CIGS heterojunction has great potential in novel applications for piezophototronic sensors and also gives a hint to modulate the performance of other multilayer heterostructures via the piezotronic effect.