Developing Hole Selective Layers and Implementing Large-size Organic Cations for Perovskite Solar Cells

Abstract

Thesis Abstract Organic-inorganic halide perovskite solar cells(PSCs) have emerged as one of the best candidates in next generation photovoltaics since their introduction in 2009. The power conversion efficiency (PCE) has dramatically increased from 3.8% to 25.7% in a decade. However, due to their limited device stability, the path to commercialization has been hindered, despite excellent PCEs. The highest performing PSCs is composed of several layers such as electron transport layers, an n-type mesoporous TiO2 layer, a perovskite layer, a hole transporting layer and a metal electrode. The high PCE can be achieved by effectively extracting and collecting the photo generated holes and selectively reducing the charge recombination loss. The state-of-art Spiro-OMeTAD is themost commonly used hole transporting material in the literature,however, its high cost due to multistep synthesis process, complex purification and instability caused by adding of hygroscopic p-typedopants, hinders the large-scale industrialization of PSCs. Thus, thedevelopment of new designed HTMs is highly desired.Additionally, the dimensionality of the perovskite influences the performance and stability of the PSCs. The reduction of dimensionality to produce lower-dimensional perovskites or analternative approach to implement an interfacial layer of the least amount of large organic cation to 3D perovskite surface to form bilayer or layered/3D mixed dimensional perovskites greatlyenhance the photovoltaic performance and stability of PSCs.Thus, the studies in this thesis aim to develop new hole-transporting materials that would be inexpensive and easily synthesizable andcan be effectively implemented for PSC applications. A series ofHTMs based on small molecules were designed and synthesized and investigated to understand the behaviour as a charge selective layerin PSCs, to further reduce the cost and improve the stability.Further more, the thesis discusses the work on the dimensionality of the perovskite and interface engineering of the perovskite absorber layer with large organic cations for improved performance and longterm stability purposes.Thus, the thesis aims to discuss the studies and investigations on themolecularly designed hole-transporting materials (HTMs) andemploy the large-size organic cation as an interface layer or dopingto form reduced mixed-dimensional perovskite absorber forenhancing the overall performance and long-term stability of thePSCs.