Ultralow dark current in near-infrared perovskite photodiodes by reducing charge injection and interfacial charge generation

Abstract

Metal halide perovskite photodiodes (PPDs) offer high responsivity and broad spectral sensitivity, making them attractive for low-cost visible and near-infrared sensing. A significant challenge in achieving high detectivity in PPDs is lowering the dark current density (JD) and noise current (in). This is commonly accomplished using charge-blocking layers to reduce charge injection. By analyzing the temperature dependence of JD 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. The interfacial energy offset between the EBL and the perovskite determines the magnitude and activation energy of JD. By increasing this offset we realized a PPD with ultralow JD and in 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.

Multidimensional Perovskites for High Detectivity Photodiodes

“…The mean J D values are reproduced over several devices (Figure S2, Supporting Information).These values are almost one order of magnitude lower than the ones measured for 3D perovskites CsFAMA and FAMA (1 × 10 −6 and 6 × 10 −7 mA cm −2 , respectively) and are ranked among the lowest reported in the literature for quasi‐2D and 3D PPDs. [ 8,9,16,17,24 ]…”

“…This approach enables EQEs ≈80% and spectral responsivity (SR) ≈0.4 A W −1 (Figure S9, Supporting Information). The interfacial energy Φ of such combinations is in fact maximized beyond that of PPDs employing only 2D–3D perovskites due to deep EBL HOMO energy (≈−5.45 eV for PTAA:poly‐TPD compared to −5.2 eV for PTAA [ 9 ] ) and the J D is suppressed to extremely low values. A reproducible and record‐low J D of 1 × 10 −8 mA cm −2 and ≈5 × 10 −9 mA cm −2 at −0.2 V was measured for BA < n > = 4 and 5, respectively (Figure 5a; Figure S10, Supporting Information) based on constant voltage measurements over time at discrete biases (Figure S11, Supporting Information).…”

“…[ 8 ] In previous work, we have shown that high‐detectivity photodiodes can be achieved by minimizing the dark current density ( J D ), and thus i n , of 3D PPDs by using appropriate blocking layers. [ 9 ] When charge injection is suppressed, J D and i n are determined by thermal charge generation at the interface between the electron‐blocking layer (EBL) and the perovskite layer, and exponentially depend on the energy offset between the highest occupied molecular orbital (HOMO) of the EBL ( E HOMO, EBL ) and the conduction band minimum (CBM) of perovskite ( E C, PVK ), that is, Φ = E C, PVK − E HOMO, EBL . Increasing Φ reduces J D and i n , and thus improves D * .…”

Semitransparent near-infrared Sn–Pb hybrid perovskite photodetectors

“…The energy levels of the perovskite layer are previously reported in literature. 45 PEDOT:PSS and C 60 /BCP were chosen as hole and electron transport layers, respectively, as they have shown to be good candidates for these roles in Sn–Pb based solar cells. 46 Usually, ITO top electrodes are processed by ion sputtering which can easily damage any soft organic underlayers, 47 leading to increased leakage current, as well as reduced efficiency and lower lifetime of the device.…”

“…Recently it has been shown that the origin of the dark current in perovskite photodetectors is due to the interfacial energy offset between the perovskite and the electron blocking layer (EBL). 45 Carefully choosing an EBL with a lower highest occupied molecular orbital (HOMO) than PEDOT:PSS ( e.g. poly(4-butyl- N , N -diphenylaniline) (poly-TPD)) could further improve the J D of these devices and will be subject of further study.…”