Effect of Cu/In stoichiometric ratio on the performance of Self-powered Dual-wavelength CuxIn2-xS2/TiO2 photodetectors

Self-powered photodetectors (PDs) play an important role in future optoelectronic devices due to their unique advantages of low energy consumption, independent operation, easy miniaturization and integration. The II-type CuxIn2-xS2/TiO2 heterojunctions (0.8 < x < 1.1) PDs demonstrate self-powered dual-wavelength photoresponse at UV and visible regions. The Cu/In ratio in CuxIn2-xS2 films can regulate the energy band structure, then the optical and electronic properties. With the Cu/In ratio increasing, the optical band-gap narrows and Fermi en-ergy level reduces for CuxIn2-xS2 films, resulting in the increased built-in electric field and the decreased interface transfer resistance for CuxIn2-xS2/TiO2 heterojunctions, which can promote the separation and transmission ef-ficiency of the photogenerated carriers and significantly improved the self-powered PDs performance. The optimized PDs with Cu1.1In0.9S2/TiO2 heterojunctions exhibit the maximum responsivity (R) of 0.79 A/W, detectivity (D*) of 4.6 x 1012, linear dynamic range (LDR) of 88 dB and sensitivity (S) of 2.6 x 104 under UV light illumination and zero bias. The CuxIn2-xS2/TiO2 PDs hold potential prospects in dual-wavelength opto-electronic applications in self-powered systems and processes.