Spontaneous Configurational Evolution Induced By An In-situ Self-formed CuI Layer In Perovskite Solar Cells

Perovskite solar cell(PSC)developed from traditional dye-sensitized solar cell(DSSC)and became a new type organic-inorganic cell.The name come from the light harvest materials CH3NH3PbX3(X=I、Br、Cl),which have perovskite crystal structure.From 2009,the development of perovskite solar was very fast and the trial power conversion efficiency(PCE)have reached surprisingly 22.1%.As representative material,CH3NH3PbI3 has much good photoelectric features,such as direct band gap semiconductor,narrower band gap width,higher light absorption coefficient,broader spectral absorption range,higher carrier mobility and long carrier diffusion lengths and ambipolar charge transport etc.In addition,the materials can be easily prepared by solution processing.For the past few years,perovskite solar cells have become one hot point in the field of physics,material science and photovoltaic device.Most efficient perovskite solar cells contain expensive organic hole transporting materials(HTM),such as spiro-OMeTAD.Also,they may contain noble metals,such as Au and Ag.These materials will improve the cost of perovskite solar cells and the using of organic HTM will reduce the chemical stability of perovskite solar cells.In order to handle these problems,researchers tried many effective methods including fabricating HTM-free perovskite solar cells,using low-cost inorganic materials(CuI,CuSCN,NiO and Cu2O)as HTM and using cheaper materials(C,Ni and Cu)as cathode.In this research,we fabricated HTM-free perovskite solar cells with Cu cathode,trying to combine the HTM-free fabrication with non-noble metal cathode,which could reduce the cost of perovskite solar cells as much as possible.Unfortunately,the PCE of fresh cells was very bad,only about 0.1%.However,the PCE of cells,which were aged of several days,was unexpectedly improved.After systematic research,we find that the PCE of cells increased gradually in a certain period.CH3NH3PbI3 and Cu cathode could react and in situ produce a layer of p-type CuI as HTM,which induced the transforming of cells from the HTM-free one to the HTM-contained one and resulted in the optimization of cells’ configuration and PCE.This work positively utilized the harmful corrosive effect of CH3NH3PbI3 to Cu cathode,which could provide a new idea of fabricating perovskite solar cells and other devices.