Research On Interface Regulation For High Performace Perovskite Solar Cells

The hybrid perovskite materials show great potential in optoelectronic device due to their high optical absorption coefficient,low exciton binding energy,ultra-long carrier diffusion length,high charge mobility and low-temperature solution method.Till now,perovskite solar cells（PSC）have attracted extensive interest attributed to the rapidly increased power conversion efficiency（PCE）.However,the PCE of PSCs still lags behind the theoretical limit efficiency,and its undesirable stability is also the biggest obstacle for its industrialization.For PSC devices,the interface plays a critical role in device performance and stability.This is mainly because the surface defect density is much higher than that of the bulk,the surface defects are mainly deep-level defects.In addition,the interface band alignment will also affect charge transport and recombination process.Although a lot of work has been devoted to surface and interface modification,which have achieved improved device performance,there is still a lack of systematic research on the micro mechanism.In view of this,this paper takes planar PSCs as the research object and utilizes various surface/interface regulating strageties in devices,the relevant micro modification mechanisms are also proposed and applied to improve the device performance and stability of our PSCs,the main research contents and results are as follows:（1）In order to improve the electrical properties of PTAA films and promote the charge transport and extraction at the PTAA/perovskite interface,two-dimensional material black phosphorus（BP）was added into the precursor solution of PTAA successfully.BP:PTAA film shows higher hole mobility and conductivity,which promote the extraction and transport of photogenerated holes at HTL/perovskite interface.By doping BP,the crystallinity of methylamine lead triiodide（MAPb I₃）perovskite film disposited on BP:PTAA was increased.The above benfits make the PCE of the p-i-n structured device based on BP:PTAA layer reach 20.49%,which is equivalent to the effect of the commonly used additive F4-TCNQ.Additionally,the BP:PTAA based device retains over 80%of the initial PCE after 800 h storage under RH of～45%.Moreover,the changes of electronic band structure in BP:PTAA was studied,and the p-type doping effect was revealed.（2）To passivate the deleterious surface defects on MAPb I₃ perovskite films,2,2-difluoroethylammonium bromine（2FEABr）was selected to treat the perovskite films surface.The spatial distribution of 2FEA⁺and Br^-ions and related surface passivation mechanism was studied respectively.Furthermore,by analyzing the dynamics of MA⁺from ~2H SS-NMR,the subtle lattice deformation in 2FEABr treated perovskite film is revealed,which reflects the firmed perovskite lattice.The increased lattice rigidity indicates suppressed electron-phonon interaction in the perovskite film.The above mechanisms contribute to the reduced non-radiative charge recombination,and the obtained PCE increases from 19.44%to 21.06%for p-i-n structured device based on2FEABr treatment.Meanwhile,thanks to the effect of“locked lattice cage”caused by the subtle lattice deformation,the humidity and thermal stability of the device are significantly improved.（3）Based on the mechanism of enhanced lattice rigidity proposed from（2）,dimethylamine bromide（DMABr）is ultilized to post-treat the Cs FA-based perovskite films.Different from 2FEA⁺,DMA⁺cations can be doped into lattice and occupy A-sites.When the treatment concentration is 0.05 mg m L^-1,it can effectively reduce the non-radiation recombination loss and have negligible effect on the bandgap.Due to the synergistic effect of small Cs⁺and large DMA⁺,the disorder degree of the system is enhanced,so theαtoδphase transition of perovskite film is inhibited at a certain extent.As a result,the n-i-p device with DMABr treated Cs FA perovskite layer realizes an improved PCE of 20.57%.The device retains over 80%of the initial PCE after 300 h storage at a RH of～50%environment,implying better humidity stability,which is mainly resulted from the improved stability of black phase.（4）The asymmetric large cation 3-methylpyridinium(3AMPY²⁺)is used as the organic ligand to post-treated Cs FA-based perovskite film surface.The introduction of ultrathin two-dimensional Dion-Jacobson（DJ）phase perovskite is confirmed and the3D/2D heterojunction is constructed successfully.Benefit from the DJ phase ultrathin2D perovskite layer,the surface defects are effectively passivated and the interface band alignment is tuned better.The PSC utilizing 3D/2D perovskite heterojunction as absorber realized a PCE over 21%,and～80%of its initial PCE is still maintained after storing for 500 h under RH of 40%.