A theoretical model for describing the bias-dependent transient behavior of dark current in multilayer (n-i-p) amorphous selenium (a-Se) detectors has been developed. The transient dark currents in these detectors are measured and are compared to the proposed dark current model. It has been found that the dark current is mainly controlled by Schottky emission of holes from the metal/a-Se contact. The initial and steady state dark currents are mainly controlled by the barrier height and the trap centers in the n layer, respectively.

The dark current behavior under operating bias is one of the important selection criteria for an x-ray photoconductor to be usable in a practical x-ray image detector. The authors have developed an analytical model for describing the transient and steady-state behavior of dark current in n-i-type amorphous selenium (a-Se) detectors by considering carrier injections from the metal contacts and thermally generated carriers. It has been found that the thermal generation current is almost two orders of magnitude smaller than the total steady-state dark current in n-i-type a-Se detectors. The main source of dark current is the injection of holes from the metal/n-layer interface which is described by the diffusion theory. The hole injection from the metal depends on the blocking layer (n-layer) thickness, the concentration of trap centers in the blocking layer, the characteristic carrier release time, and the effective barrier height. The fitting of the first principles model with the experimental results estimates the concentration of deep hole trap center in the n-layer, the trap depth from the valence band edge, and the effective barrier heights for the injecting carriers. The electron injection varies with the work function of the contact metal.

Organo-halide perovskites in planar heterojunction architecture have shown considerable promise as efficient light harvesters in solar cells. We carry out a numerical modeling of a planar lead based perovskite solar cell (PSC) with Cu2ZnSnS4 (CZTS) as the hole transporting material (HTM) using the one-dimensional solar cell capacitance simulator (SCAPS-1D). The effects of numerous parameters such as defect density, thickness, and doping density of the absorber layer on the device performance are investigated. The doping densities and electron affinities of the electron transporting material (ETM) and the HTM are also varied to optimize the PSC performance. It has been observed that a thinner absorber layer of ∼220 nm with a defect density of 1014 cm−3 compared to the reference structure improves the device performance. When doping density of the absorber layer increases beyond 2 × 1016 cm−3, the power conversion efficiency (PCE) reduces due to enhanced recombination rate. The defect density at the absorber/ETM interface reduces the PCE as well. Considering a series resistance of 5 Ω · cm2 and all the optimum parameters of absorber, ETM and HTM layers simultaneously, the overall PCE of the device increases significantly. In comparison with the reference structure, the PCE of the optimized device has been increased from 12.76% to 22.7%, and hence the optimized CZTS based PSC is highly efficient.

Methylammonium lead halide ( M A P b I 3 ) is widely used as perovskite absorber material in thin-film solar cell technology because of its eminent cell performance. Recently, formamidinium lead iodide perovskite ( F A P b I 3 ) has received great attention because of its optimum bandgap value closer to the infrared single junction range. In this paper, a suitable combination of hole transporting material (HTM) and electron transporting material (ETM) is determined to achieve higher efficiency compared to existing structures utilizing an F A P b I 3 absorber. The proposed structure uses two stable metal oxides as HTM ( N i O X ) and ETM ( S n O 2 ). A comparative numerical analysis of solar cell performance is shown among four different HTM materials using the Solar Cell Capacitor Simulator (SCAPS-1D). Performance evaluation is also carried out for three different compositions of F A P b I 3 having different band gaps with respect to absorber thickness. Optimized absorber thickness, HTM and ETM doping density, and absorber defect density are enumerated using numerical simulation. By deploying the optimized parameters, maximum power conversion efficiency is found to be 26.23%. Later on, effects of R s e r i e s and R s h u n t on ideal solar cell performance are analyzed using numerical simulation.

No abstract