Additive Conformational Engineering To Improve the PbI2 Framework for Efficient and Stable Perovskite Solar Cells

Prediction and simulation of a potential barrier block in Van der Waals heterojunction photodetectors

The pBp structure can effectively suppress the dark current of a photodetector by blocking the majority of carriers. However, it is a big challenge to carry out large-scale simulation optimization for two-dimensional (2D) pBp heterojunction photodetectors due to a lack of the device models. Here, a numerical simulation model of the 2D pBp heterojunction was established based on the finite element method to solve this problem. Using this model, the spatial distribution of the energy band is clarified for each layer. The concentration of nonuniformly distributed electrons, induced by the incident light and bias voltage, is obtained by solving the diffusion and drift equations. The characteristics of the photocurrent and the dark current could be presented and the quantum efficiency could be calculated by counting the ratio of the number of carriers collected at the terminals and the carriers photogenerated. The material parameters could be modified for the optimization of the simulation and prediction. In using our model, a B P/M o S 2/graphene photodetector was constructed, and the simulation results show that it works effectively under a reverse bias ranging from -0.3 to 0 V. The external quantum efficiency is 18%, while the internal efficiency approaches 85%. The doping in the barrier region definitely does not affect the dark current and the photocurrent. These results are similar to experimental results published earlier. In addition, with the BP bandgap width of 0.8 eV and incident wavelength of 1.7 µm, the dark current density predicted by the model could reach 3.3×10-8 A/c m 2, which is two orders lower than the reported 2D photodetectors at room temperature. This proposed model provides a way to design 2D pBp heterojunction photodetectors.

Morphological investigation and 3D simulation of plasmonic nanostructures to improve the efficiency of perovskite solar cells

The light absorption process is a key factor in improving the performance of perovskite solar cells (PSCs). Using arrays of metal nanostructures on semiconductors such as perovskite (CH3NH3PbI3), the amount of light absorption in these layers is significantly increased. Metal nanostructures have been considered for their ability to excite plasmons (collective oscillations of free electrons). Noble metal nanoparticles placed inside solar cells, by increasing the scattering of the incident light, effectively increase the optical absorption inside PSCs; this in turn increases the electric current generated in the photovoltaic device. In this work, by calculating the cross-sectional area of dispersion and absorption on gold (Au) nanoparticles, the effects of the position of nanoparticles in the active layer (AL) and their morphology on the increase of absorption within the PSC are investigated. The optimal position of the plasmonic nanoparticle was obtained in the middle of the AL using a three-dimensional simulation method. Then, three different morphologies of nano-sphere, nano-star and nano-cubes were investigated, where the short-circuit currents (Jsc) for these three nanostructures were obtained equal to 19.01, 18.66 and 20.03 mA/cm2, respectively. In our study, the best morphology of the nanostructure according to the Jsc value was related to the nano-cube, in which the device power conversion efficiency was equal to 16.20%, which is about 15% better than the PSC with the planar architecture.