Self-powered hybrid humidity sensor and dual-band UV photodetector fabricated on back-contact photovoltaic cell

Self-powered multi-functional sensors were fabricated by integrating a crystalline Si interdigitated back-contact (IBC) photovoltaic (PV) cell with a vertically stacked structure into a single chip. The IBC PV cell was vertically connected with a humidity sensor and a photodetector (PD) in parallel. The measured humidity current of the WO3 thin-film humidity sensor increased monotonically when the relative humidity was increased from 30% to 95%. In addition, the humidity characteristics of the unannealed WO3 thin-film humidity sensor were better than those of the annealed samples. The cutoff wavelengths of WO3 and Ga2O3 thin-film PDs were around 370 and 250 nm, respectively. The measured responsivity of WO3 and Ga2O3 thin-film PDs at the cutoff wavelength were 1.7 × 10−7 and 9.8 × 10−7 A/W, respectively, under 1-sun illumination.