Perovskite solar cells (PSCs) have emerged as a promising candidate for addressing the energy crisis due to their rapid efficiency improvement up to 24.2% within 10 years. One of the most challenging obstacles to commercialization of PSCs is their instability toward environmental conditions. Lead-free, halide-based perovskites are drawing appreciable attention for solar cell applications due to the non-toxic nature and stable performance in ambient environment. With the aim of improving reproducibility and spectral properties of the devices, in the last three years the scientific community strongly focused on Caesium-doping for hybrid (typically, organolead) perovskites. In parallel, in order to further contrast hygroscopicity and reach thermal stability, research has also been carried out to achieve the development of all-inorganic perovskites based on Caesium, the performances of which are actually rapidly increasing. This article represents the study of physical, optical, and electrical properties Caesium Titanium (IV) based single halide Perovskite absorbing material for the optimum photovoltaic application. Also in recently developed high-efficiency metal organometal halide PSCs, electron and hole transporting materials have shown key roles in determining the growth of perovskite crystals, as well as the performance and stability of the device. The utilization of polymer materials has been studied as both HTM’s and ETM’s but with little effectiveness, typically resulting in a lower conversion efficiency. But some other materials such as Spiro-OMeTAD requires comparable dopants and additives, which is a source of perovskite instability and also it requires very high design costs ; which all leads to the idea of alternate transport materials. In this study, a numerical simulation analysis on the PSCs performance with Graphene Oxide (GO) as HTM is conducted. We investigated GO/Cs₂TiBr₆/ TiO₂ structure (Figure 1) and studied the change in various photovoltaic parameters with the change in different input factors. The deep understanding of operation mechanism of PSCs is essential and required to furtherly improve device performance. Therefore, Solar Cell Capacitance Simulator (SCAPS-1D), a device simulator widely using in inorganic solar cells, was employed to controllably design PSCs. This simulator package basically uses the poisons equation, the drift and diffusion carrier equation and the continuity equation to solve for various input parameters. It has numerous advantages than any other simulators available in the market like incorporating the interface defect densities, simulation of devices with up to 7 layers in a single run etc. The influence of thickness of the absorber layer, the hole transport layer, defect density of two interfaces ( perovskite/ETL and HTL/perovskite), band gap of absorber layer, electron affinity of both absorber and ETL , finally the temperature and parasitic resistance ( series and shunt ) of the lead-free device is studied. The main objective of the study was the exploration of the effect and efficiency of Graphene Oxide (GO) and the Hole transport layer (HTL) on the performance of the proposed Caesium based heterojunction solar cell.

The simulation was carried out in the standard operation conditions for SCAPS-1D. The optimized thickness values for maximum PCE value are observed to be 1 μm for absorber, 0.1 μm for HTL. The performance of the device deteriorated when the defect density value increases for both interfaces and was found that that the front interface density should be less than 1E16 and the back interface density less than 1E10 for optimum performance. It can be attributed due to larger number of recombinations at these interfaces. The performance decreased with the increase in operating temperature range and also with the increase in parasitic resistances as expected. Finally the electron affinity of the absorber seems to be not much involved with the inner working of the device as the parameters almost remained constant with a change in it.

The elicited results suggest that Cs₂TiBr₆ can play a momentous role as an absorbing perovskite towards the highly efficient lead-free all-inorganic perovskite solar cell technology .The findings also reveal that the GO could be a promising HTL for the fabrication of low cost, high efficiency Caesium based heterojunction solar cell. In the future, this efficiency may offer prominent potential as a substitute in a highly efficient green solar absorber material for photovoltaic applications after confirmation in the laboratory.