Polymer As Transporting Materials In Perovskite Solar Cells

Perovskite solar cells have attracted remarkable attentions during the past five years due to the good optoelectronic properties of perovskite semiconductor and their high device power conversion efficiency. Different materials and fabrication techniques applied in organic solar cells(OPV) or dye-sensitized solar cells have been introduced into perovskite solar cells and a lot of progresses have been achieved. This thesis summarizes the development of the normal and inverted perovskite solar cell first. And then the application of electron transporting materials(ETM) and hole transporting materials(HTM) in perovskite solar cells are systematically studied.PCBM and some C60 derivatives are the most common ETMs used in inverted perovskite solar cell. However, these small molecules have disadvantages such as weak light absorption, untunable energy level, and difficult to pure, which limits their further applications. This thesis presents decent PCE by applying polymer as ETM(N2200 etc.) in perovskite solar cell to replace the PCBM, resulting in PCE comparable to the PCBM devices. The device parameters show that the decreased fill factor lead to the decreased device performance. And the impedance investigations demonstrates that the N2200 device possess a much lower recombination resistance than the PCBM device, resulting in a high exciton recombination rate, which could mainly account for its low FF. Moreover, to further demonstrate the universality of organic polymer as a new class of ETM in perovskite solar cells, two other polymers PNVT-8 and PNDI2OD-TT, have also been tested, and fair device performances have been achieved respectively.Spiro-OMeTAD and its derivatives are the most common and high efficient HTMs in perovskite solar cell. However, most of these HTMs need additives to increase the device performance by increasing the hole mobility. We applied polymer HTMs without any dopants into perovskite solar cells, and we got the PCE of 7.14% for the devices. Based on these studies of the optoelectronic properties of materials and the device performance, we conclude that HTMs with low highest occupied molecular orbital(HOMO) level, high lowest unoccupied molecular orbital(LUMO) level and high hole-mobility are ideal to obtain efficient perovskite solar cells.