Transport properties of CuIn1−xAlxSe2/AZnO heterostructure for low cost thin film photovoltaics

Abstract

CuIn_1−xAl_xSe₂ (CIASe) thin films were grown by a simple sol–gel route followed by annealing under vacuum. Parameters related to the spin–orbit (Δ_SO) and crystal field (Δ_CF) were determined using a quasi-cubic model. Highly oriented (002) aluminum doped (2%) ZnO, 100 nm thin films, were co-sputtered for CuIn_1−xAl_xSe₂/AZnO based solar cells. Barrier height and ideality factor varied from 0.63 eV to 0.51 eV and 1.3186 to 2.095 in the dark and under 1.38 A.M 1.5 solar illumination respectively. Current–voltage characteristics carried out at 300 K were confined to a triangle, exhibiting three limiting conduction mechanisms: Ohms law, trap-filled limit curve and SCLC, with 0.2 V being the cross-over voltage, for a quadratic transition from Ohm's to Child's law. Visible photodetection was demonstrated with a CIASe/AZO photodiode configuration. Photocurrent was enhanced by one order from 3 × 10⁻³ A in the dark at 1 V to 3 × 10⁻² A upon 1.38 sun illumination. The optimized photodiode exhibits an external quantum efficiency of over 32% to 10% from 350 to 1100 nm at high intensity 17.99 mW cm⁻² solar illumination. High responsivity R_λ ∼ 920 A W⁻¹, sensitivity S ∼ 9.0, specific detectivity D^* ∼ 3 × 10¹⁴ Jones, make CIASe a potential absorber for enhancing the forthcoming technological applications of photodetection.