Toward The Development Of Printable Perovskite Solar Cells

Abstract

PSCs have become a significant performer in third generation photovoltaics with power conversion efficiency, greater than 22% for active areas less than 1 cm2. However, with efficiency improvement, concerns regarding the operational stability and industrial production firstly resolved to grow into commercially viable PSCs. To address above stated issues most stable, yet efficient Monolithic PSCs (mPSCs) are structured. The mPSCs are having compact TiO2, mesoporous TiO2, mesoporous ZrO2, and mesoporous carbon electrode layers in optimal thicknesses on the FTO substrate. Fabrication protocol for all the layers which is easily scalable for large area mPSCs manufacturing is highly required. Furthermore top carbon electrode materials those are stable and behaves as protective casing to make PSCs stable has also been highly desired. Hence, in this project our aim is to optimize top carbon layer and study photophysical processes inside the mPSCs. This research work is mainly divided into three parts. The first part of the dissertation described carbon film fabrication by screen printing technique and their investigation at different annealing temperature . Influence of annealing temperatures on the electrical, morphological and structural properties of the carbon film has been discussed. It is shown that a low annealing temperature is good for better adherence of the conductive carbon films, however, temperatures higher than 300°C are required to produce efficient mPSCs. A sintering temperature of 400°C showed the highest device efficiency of 13.2%. It is important to correlate all the physical properties/processes taking place in the mPSCs to gain a deeper understanding of mPSCs operation: What is the role of the contacts? What limits the efficiency of existing perovskite solar cells? How many charge carriers are there in the cell under operating condition. Hence, in second part, Electrochemical Impedance spectroscopy (EIS) spectrum has been described, which is performed on the mPSCs having highest efficiency during previous experiments. The EIS spectrum of mPSCs quantitatively explains the role of contacts, layers, charge generation, drift and diffusion of charge carriers and recombination. This would further provide insight into the performance-limiting physical processes of mPSCs. The microstructure or morphology of the perovskite crystals inside mesoporous TiO2 and mesoporous ZrO2 have significant effect on the mPSCs performance and stability. Therefore, to achieve higher mPSCs device performance, one-dimensional microrods (4mm-5mm) of PbI2 and CH3NH3PbI3 (MAPbI3) is fabricated in the 3rd part. These microrods consist of unique structural and morphological properties which are grown at room temperature. The XRD and TEM analyses confirm the existence of strong interactions between different stable groups in the crystals. The morphological studies approve crack free morphology of PbI2 and MAPbI3 micro-rods. The above results are expected to have a big effect on solar cell and photo-detection industry by fostering improvement of thin-film opto-electronic devices.