Self-powered FTO/amorphous-(In_0.23Ga_0.77)₂O₃/spiro-OMeTAD ultraviolet photodetector with broadband responsivity and wavelength discrimination capability

In this work, FTO/amorphous-(In_0.23Ga_0.77)₂O₃/spiro-OMeTAD photodetector capable of broadband detection (200–400 nm) with wavelength discrimination is fabricated. Incorporation of spiro-OMeTAD as hole transport layer improved self-powered performance of FTO/amorphous-(In_0.23Ga_0.77)₂O₃/spiro-OMeTAD broadband photodetector. Under 260 nm illumination, the photodetector exhibited a responsivity (R) of 0.63 mA/W and a detectivity (D^*) of 5.40 × 10¹⁰ cm Hz^1/2 W⁻¹ under zero bias. The values enhanced to R = 0.61 mA/W and D^* = 5.50 × 10¹⁰ cm Hz^1/2 W⁻¹ under 320 nm illumination. For 400 nm illumination, the values were R = 0.35 mA/W, D^* = 4.90 × 10¹⁰ cm Hz^1/2 W⁻¹ under zero bias. Moreover, FTO/amorphous-(In_0.23Ga_0.77)₂O₃/spiro-OMeTAD photodetector demonstrated faster response speed with rising time decreased to 0.02 s and decay time decreased to 0.04 s, compared to FTO/amorphous-(In_0.23Ga_0.77)₂O₃ photodetectors under 260 nm illumination. The wavelength discrimination capability within 200–400 nm range was attributed to type-I staggered band alignment in FTO/amorphous-(In_0.23Ga_0.77)₂O₃ interface and type-Ⅱ staggered band alignment in spiro-OMeTAD/amorphous-(In_0.23Ga_0.77)₂O₃ interface, through choosing illumination on FTO or spiro-OMeTAD sides. In conclusion, FTO/amorphous-(In_0.23Ga_0.77)₂O₃/spiro-OMeTAD heterogeneous junction, using a combination of p-type polymer and inorganic wide bandgap semiconductors, shows great potential for self-powered and high-performance broadband photodetectors.