Guanidine-based Molecular Interface Modifier For Efficient And Stable Inverted Perovskite Solar Cells

Since Miyasaka et al.reported the application of perovskite materials in dye-sensitized solar cells in 2009,the research of perovskite solar cells（PSCs）has made rapid progress.So far,the power conversion efficiency（PCE）of PSCs has reached 25.7%,exceeding the second-generation solar cells represented by cadmium telluride（Cd Te）and indium phosphide（In P）.Among all kinds of device architectures of PSCs,the inverted planar PSCs have drawn wide attention mainly due to their advantages of simple preparation,low hysteresis effect and low cost.However,the perovskite polycrystalline films prepared by the low temperature solution method have a large number of defects on the surface and grain boundaries,which lead to the non-radiative recombination of carriers at the device interface and reduce the device performance.Therefore,in this thesis,two kinds of compounds with biguanide groups,i.e.N,N-Dimethylimidodicarbonimidic diamide（DMID）and dimethylbiguanide halides,are introduced into the perovskite layer/electron transport layer interfaces to fabricate efficient and stable inverted planar PSCs.The effects of the inclusion of these interface modification layers on the interfacial energy level alignment,defect passivation,carrier transport and extraction,as well as the performance of PSCs are investigated.The main research contents are as follows:Firstly,DMID is applied to modify the interface of Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃perovskite layers/PC₆₁BM electrons transport layers.The results show that the DMID interface modifier containing two guanidine groups can form interaction with the uncoordinated Pb²⁺ions in the perovskites,which is beneficial to improve the crystallinity and average grain size of the perovskite films.In addition,the inclusion of DMID interface modifier can reduce the surface defects of perovskite films,optimize the energy level alignment of perovskite films and PC₆₁BM electron-transport layers,thus improving the carrier transportation and collection at the interface.The PSCs modified with DMID(concentration of 0.08mg m L^-1)exhibit the best PCE of 19.42%with the superior humidity stability.Secondly,dimethylbiguanide halides,including DMID·HI,DMID·HBr and DMID·HCl,areintroducedtomodifytheinterfaceof Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃perovskite layers/PC₆₁BM electrons transport layers.The results show that the guanidine cations and halogen anions in DMID·HX can interact with the Pb²⁺ions and I^-in the perovskites,improving the crystallinity and reducing the surface roughness of perovskite films.Meanwhile,the defect densities of the perovskite films are significantly decreased upon incorporating dimethylbiguanide halides,which promotes the carrier transport and extraction.In addition,it is found that the device with DMID·HCl shows the best PCE of 20.34%,along with a high V_ocof 1.14V.Moreover,PSCs based on DMID·HCl modification can maintain over 80%of the initial PCE after being storage for 30 days under dark conditions with a relative humidity of 60±5%at 25℃.Our work provides a novel interface engineering using the biguanidine-based compounds,which provides a new strategy for improving the efficiency and stability of inverted planar PSCs.