These charge-blocking layers increase the energy barrier for undesired charge injection, which occurs from the electrodes into the light-absorbing semiconductor layer under reverse bias. Besides material driven strategies including the use of antioxidant additives 20, 21, prevention of shunt paths 22, control of film crystallization 23, and passivation of traps 24, 25, the use of hole-blocking and electron-blocking layers (HBLs and EBLs) has been demonstrated to be critical for the control of J D 26, 27, 28, 29. Over recent years, significant efforts have been devoted to minimizing the dark current in thin film perovskite photodiodes. Collectively, these factors increase J D and the device noise current level ( i n) thus limiting the specific detectivity ( D *), a key figure of merit that describes the smallest detectable signal.
This unwanted property has been attributed to the susceptibility of divalent Sn to oxidation 18, charge injection from the contacts as well as structural and compositional imperfections in the material, leading to pinholes, trap states, and grain boundary leakage 19. However, to date Pb and mixed Pb–Sn-based perovskite photodiodes (PPDs) have suffered from relatively high dark currents. Notably, alloying lead halide perovskites with tin extends the detection range further into the NIR, with absorption wavelengths up to 1050 nm 17. Additional benefits include low processing temperature, and an optical absorption spectral range that can be tuned through structural and compositional modification 14, 15, 16. Their high carrier mobility, long electron-hole diffusion lengths, and low exciton binding energy 6, 7, 8 enable high and fast responsivity to light 9, 10, 11, 12, 13. Metal halide perovskites are solution processable semiconducting materials that have attracted extensive interest for their remarkable photovoltaic properties 4, 5, but are likewise promising candidates for photodiodes. Minimizing the dark current density ( J D) of emerging thin film flexible photodiodes is essential for near-infrared (NIR) sensing and imaging 1, 2, 3. By increasing this offset we realized a PPD with ultralow J D and i n of 5 × 10 −8 mA cm −2 and 2 × 10 −14 A Hz −1/2, respectively, and wavelength sensitivity up to 1050 nm, establishing a new design principle to maximize detectivity in perovskite photodiodes. The interfacial energy offset between the EBL and the perovskite determines the magnitude and activation energy of J D. By analyzing the temperature dependence of J D for lead-tin based PPDs with different bandgaps and electron-blocking layers (EBL), we demonstrate that while EBLs eliminate electron injection, they facilitate undesired thermal charge generation at the EBL-perovskite interface. This is commonly accomplished using charge-blocking layers to reduce charge injection.
A significant challenge in achieving high detectivity in PPDs is lowering the dark current density ( J D) and noise current ( i n). Metal halide perovskite photodiodes (PPDs) offer high responsivity and broad spectral sensitivity, making them attractive for low-cost visible and near-infrared sensing.
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