Device Engineering And Mechanism Studies Of Perovskite And Organic Solar Cells

Clean and renewable energy sources are urgently needed as the current world now is facing the energy crisis as well as the increasingly severe pollution caused by the burning of traditional fossil fuels.To develop new renewable resources,photovoltaics(PVs)have been investigated extensively for several decades though high performance GaAs solar cells have already been successfully deployed in outer space,affordable solar panels for domestic use still have a long way to go.Hybrid organic-inorganic perovskite solar cells,as one of the most promising third-generation thin film PVs,have attracted tremendous attention in the past seven years due to their high efficiency,low price of raw materials and easy of fabrication.Although a power conversion efficiency of 20%has been achieved for perovskite solar cells,stability issue still hinders the development of PVs towards household solar panels.Thus,in the first part of my thesis I try to fabricate stable and high efficiency perovskite solar cells with an inverted structure.The device configuration includes:transparent conducting layer,hole transport layer(HTL),perovskite layer,electron transport layer(ETL)and back contact.I mainly focus on the device engineering of the hole transport and perovskite layer to achieve high efficiency and stable perovskite solar cells.Main research results are as followed:1.Pioneering works on the fabrication and characterization of inverted planar perovskite solar cells are introduced,including the preparation of high-quality perovskite films via different deposition techniques such as pressure induced crystallization method and solvent assited annealing techniques;utilizing scanning electron microspectroscopy(SEM)and X-ray powder diffraction(XRD)etc to investigate the suface properties of perovskite films.We found that new deposition tecniques are effective in fabricating high-quality perovskite films.2.We demonstrate the work on F4-TCNQ doped PEDOT:PSS as the HTL in the inverted perovskite solar cells(MAPbI3-xClx),which exhibited a high power conversion efficiency(PCE)surpassing 17%,with increased short circuit current density(Jse)and open circuit voltage(Voc).Systematic investigations on the mechanisms for the enhancement of photovoltaic performance revealed that the improvement is mainly attributed to the enhanced electrical conductivity,favorable energy level alignment as well as efficient charge carrier dissociation with retarded recombination.This work brings wide potential applications including organic solar cells,organic light emitting diodes and organic thermoelectronics.3.We first introduced solution-processed MoSx as the hole transport layer in inverted perovskite solar cells(MAPbI3).We found that perovskite solar cells with MoSx as the HTL exhibited higher open circuit voltage(>1 V)than that with PEDOT:PSS as the HTL,which could be attributed to higher crystallinity of the perovskites deposited onto MoSx as well as better energy level alighment between the HOMO level of MoSx and perovskite film.Whats's more,the devices based on MoSx as the HTL still maintain 90%PCE of the original value after 140 h aging test under dry air,while only 60%for the controlled devices with PEDOT:PSS as the HTL.