Tuning Halide Composition Allows Low Dark Current Perovskite Photodetectors With High Specific Detectivity

Abstract

interest in both academic and industrial landscapes for a wide range of applications, including image sensing, [8] optical communication, [9] environmental monitoring, and biomedical applications. [10,11] New emerging applications require selfpowered, cost-effective, highly sensitive, and flexible devices. [12][13][14] These conditions can be fully satisfied using PDs based on perovskite active layers, which combine high ambipolar charge carrier mobility [6,15] with long carrier diffusion length, [16,17] effective light absorption, [18] high defect tolerance [19,20] and low-cost solution processability, [21] making them suitable candidates for high-performance PDs.The route to obtain highly sensitive sensors requires minimizing dark current (J d ) values, which limits the noise (i n ) in devices and maximizes light conversion. To date, few methods exist to reduce the dark current in PDs. They are based on the use of charge-blocking layers to minimize charge injection. [22,23] Other strategies are related to inclusion of additives [24,25] or controlling film crystallization [26,27] to minimize backward charge injection at the electrodes. However, there is a deficit of efforts focused on understanding the role of perovskite composition and its correlation to device J d . Tuning halide composition in perovskites isa powerful approach demonstrated to enhance the performance of perovskite photovoltaic devices where such compositional modifications drive improvements in open-circuit voltage (V oc ) and a reduction in nonradiative voltage losses. Similarly, photodetectors (PDs) operate as light to current conversion devices hence it is relevant to investigate whether performance enhancements can be achieved by similar strategies. Herein, perovskite PDs are fabricated with an inverted photodiode configuration based on a MAPb(I 1-x Br x ) 3 perovskite (MA = methylammonium) active layer over the x = 0-0.25 composition range. Interestingly, it has been found that increasing the Br content up to 0.15 (15%) leads to a significant reduction in dark current (J d ), with values as low as 1.3 × 10 −9 A cm -2 being achieved alongside a specific detectivity of 8.7 × 10 12 Jones. Significantly, it has been observed an exponential relationship between the J d of devices and their V oc over the 0-15% Br range. The superior performances of the 15% Br-containing devices are attributed to the reduction of trap states, a better charge extraction of photogenerated carriers, and an improvement in photoactive layer morphology and crystallinity.

Bidirectional and Dual‐Mode Organic Photodetector Enables Secure Ultraviolet Communication

“…Its corresponding noise current and specific detectivities are shown in Figures S3 and S4 (Supporting Information). [36][37][38] In order to deeply understand the reasons for the difference in spectral response curves, we begin with the definition of the responsivity, which represents the detective sensitivity of a photodetector, generally given by: [39,40] where I ph is the outputted photocurrent obtained under light illumination, P is the power density of the illumination light and S is the effective illumination area of the device. From the equation we can see I ph is the key factor that is intensely in positive correlation of the R λ , which is jointly dependent on the light absorption within the BHJ layer, the charge carrier generation quantum yield of the exciton and charge transfer state dissociation, and collection efficiency of the photo-generated charge carriers.…”

Enhanced sub-1 eV detection in organic photodetectors through tuning polymer energetics and microstructure

“…A well-established practice is to use HTL and electron-transporting layer to suppress parasitic currents across the device under reverse bias, which we also adopted in this work. Effective suppression of J d can also be achieved by deepening the HOMO of D or shallowing of A LUMO levels, which, unfortunately, presents a trade-off for ultralow bandgap materials ( 42 , 45 – 47 ).…”

An Organic Electrochemical Transistor Integrated Photodetector for High Quality Photoplethysmogram Signal Acquisition

“…The specific detectivity was calculated using $${D^ * } = \frac{{\sqrt {A\Delta f} }}{{NEP}}\, = \frac{{R\sqrt {A\Delta f} }}{{{i_n}}}$$, and the sensitivity was calculated using S = 20 × log 10 ( J light / J dark ) ( dB ). [ 28 ] The EQE using $$EQE\, = \,R\frac{{hc}}{{\lambda q}}$$ was determined. In these equations, J light represents light current density, J dark represents dark current density, P light represents light power density on the device, A is the effective area of the photodetector, Δ f is the bandwidth (1 Hz), NEP is the noise equivalent power, i n is the noise current, h is the Planck's constant, c is the light speed, and λ is its wavelength.…”