MODELING THE MORPHOLOGY AND ELECTRONIC PROPERTIES OF SOLUTION PROCESSED THIN FILMS AND THEIR IMPACT ON THE PERFORMANCE OF PEROVSKITE SOLAR CELLS
Taufique, Mohammad Fuad Nur
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Perovskite solar cells (PSCs), which employ solution‐processible hybrid organic‐inorganic perovskite as a photoactive material, have demonstrated outstanding power conversion efficiency and hold excellent promise as light‐weight and cost‐effective devices. PSCs comprise thin films of photoactive material along with electron transport (ETL) and hole transport layers (HTL). Controlling the morphology and quality of these individual layers and interfaces, which determine device performance, is critically important towards commercialization of PSCs. In this dissertation, we evaluated the impact of point defects present in perovskites on the electronic properties by employing density functional theory (DFT) calculations. Results from the DFT calculations suggest that the location of deep and shallow level defects depend on the topology of the exposed perovskite surfaces and can span the entire range of the band gap region. The impact of the concentration and energy states of specific point defects on the performance of PSCs was systematically determined using full-cell simulations. The results indicate a strong dependence of the cell performance on the location of defect states within the band gap. This finding presents an opportunity to tailor the solution-processing methodology to favor specific defects that are less detrimental. Another option to mitigate the detrimental impact of defects and efficiently transfer charges from perovskite to electrode is by passivating surface-defects using an ETL comprising [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). To understand the deposition mechanism of solvated PCBMs on perovskite and determine the resulting morphology we developed a multiscale model based on molecular dynamics (MD) simulations in conjunction with kinetic Monte Carlo (KMC). Results from the MD simulations suggest that the deposition of individual solvated PCBMs is dominated by entropic contribution and the deposited configuration of PCBM depends on the nature of the exposed perovskite surface as well as PCBM concentration in stock solution. Rates of different deposition events determined from MD simulations were used in the KMC model to simulate the growth rate and surface coverage of monolayers at various processing conditions. The results provide predictive correlations between processing conditions and morphology of ETLs that can passivate surface defects on perovskite and therefore immensely improve the performance of these solar cells.