Preparation And Properties On Back Electrode And Blocking Layer For Perovskite Solar Cells

As a new type of solar cell, Perovskite Solar Cells (PSCs) has received extensive attention and achieved rapid development in recent years. The back electrode and blocking layer are key components of PSCs and play important roles in the overall performance of the solar cells. Normally, Au or Ag thin film fabricated by thermal evaporation deposition is used as back electrodes. Au and Ag is expensive, so it is unsuitable for commercial and large-scale manufacture. Suitable back electrode materials can not only reduce the cost of the solar cells, but also benefit its practical application. The blocking layer is the electron collection layer, and the most common material is TiO2 nanocrystals. The compact layer is required to prevent direct contact between holes formed in the perovskite or HTM layer and fluorine-doped tin oxide (FTO) electrode for high-efficiency PSCs with various configurations. The ideal blocking layer should be dense and continuous, and has an ideal thickness. In this thesis, with the aim to improve the efficiency of PSCs, a series of studies on the back electrodes and the blocking layers are carried out. Details are listed as follows:(1) Efficient mixed halide perovskite solar cells were fabricated using thermally evaporated Ag or Ag-Al alloy layers as back electrodes. The properties of Ag-Al alloy and Ag films deposited on a hole-transport material layer for use in CH3NH3PbI3-xClx solar cells were investigated. The Ag-Al alloy layer exhibited high optical reflectivity and good adhesion on hole - transport material layer compared to a layer of Ag. Furthermore, the Ag-Al alloy based perovskite solar cell accomplished a 37.3 % enhancement in PCE compared to the optimized Ag electrode. The fabricated Ag-Al alloy perovskite cells show a fill factor of 59.6%, open-circuit voltage of 0.88 V, short-circuit current density of 21.11 mA/cm2, yielding an overall efficiency of 11.07%. The PCE enhancement mechanisms are discussed. Our work has demonstrated that Ag-Al is a promising back electrode material for high-efficiency perovskite solar cells.(2) In this study, the characteristics of TiO2 compact layer using various methods and its effects on the PV performance of perovskite solar cells were investigated. TiO2 compact layer was prepared by a sol-gel method based on titanium isopropoxide and HCl, spin-coating of titanium diisopropoxide bis(acetylacetonate), screen-printing of Dyesol’s bocking layer titania paste, and a chemical bath deposition (CBD) technique via hydrolysis of TiCl4, respectively. The morphological and micro-structural properties of the formed compact TiO2 layers were characterized by scanning electronic microscopy and X-ray diffraction. The analyses of devices performance characteristics showed that surface morphologies of TiO2 compact films played a critical role in affecting the efficiencies. The nanocrystal TiO2 film deposited via the CBD route acts as the most efficient hole-blocking layer and achieves the best performance in perovskite solar cells. The CBD-based TiO2 compact and dense layer offers a small series resistance and a large recombination resistance inside the device, and makes it possible to achieve a high power conversion efficiency of 12.80%.