Regulation Of Interface Carrier Behavior In Perovskite Solar Cells

Organic-inorganic hybrid perovskite is a class of excellent light absorption material for solar cells,owing to their appropriate band gap and remarkable optical absorptions across a wide range of the solar spectrum,high absorption coefficients,long charge carrier diffusion lengths,and low cost.Perovskite solar cells(PSCs)have been developing rapidly at an unprecedented speed since MAPbBr3 and MAPbI3 were adopted as light absorption materials in solar cells for the first time by Prof.Miyasaka in 2009,and their record power conversion efficiency(PCE)has exceeded 25%which is close to that of single crystal silicon solar cells and higher than that of polycry stalline silicon solar cells.The carrier behavior at the interface of semiconductor devices is one of the important factors affecting the device performance.This dissertation focused on the interface engineering of PSCs,passivated the defects of perovskite materials and improved the matching degree of energy levels between different functional layers through excimer laser surface modification(ELSM)and the introduction of CuCrO2 hole transport material(HTM),respectively,and the resulting performance of PSCs and the corresponding mechanisms were investigated.(1)248 nm KrF excimer laser with high photon energy and shallow penetration depth has been introduced to perform surface modification on MAPbI3 films through irradiation for the first time,and a whole ELSM process could be completed in several seconds.After ELSM,the trap density of MAPbI3 film decreased from 1.61×1016 cm-3 to 5.81×1015 cm-3 and the nonradiative recombination could be suppressed effectively.As results,the open-circuit voltage and PCE of MAPbI3 based PSCs increased from 1082±27 to 1117±16 mV and from 16.69±0.77%to 18.50±0.65%,respectively,and the PCE of the champion device reached 19.38%.Additionally,the larger charge recombination resistance,slower open-circuit photovoltage decay,and longer charge recombination lifetime confirmed the effective suppression effect of ELSM on the charge carrier recombination in PSCs.ELSM is a rapid,simple,direct,and non-contact approach for improving the performance of perovskite-based devices including PSCs.(2)Triple cation perovskite[(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08 possesses better photovoltaic performance and stability than conventional perovskite MAPbI3.The excimer laser was used to modify the triple cation perovskite films,the influence of laser energy density on the quality of perovskite films and the cell performance,and the corresponding mechanism were investigated.When the excimer laser energy density was 2.13 mJ cm-2,the triple cation perovskite film exhibited the highest photoluminescence intensity and the longest carrier lifetime,and the PCE of the corresponding PSCs was as high as 21.42%.After analyzing the composition of the triple cation perovskite films before and after ELSM,it was found that the Pb0 defects on the surface of the perovskite films can be removed by excimer laser treatment.(3)Appropriate amount of lead iodide could passivate the defecs of lead hylide perovskite films.248 nm KrF excimer laser was used to irradiate the triple cation perovskite[(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08film with no excess lead iodide in accordance with stoichinometirc ratio and induced the decompositon of perovskite producing lead iodide passivation layer.The influence of laser energy density on the quality of perovskite films and the cell performance,and the corresponding mechanism were investigated.When the excimer laser energy density was 6.67 mJ cm-2,the PCE of corresponding PSCs was as high as 21.54%,while the PCE of PSCs based on untreated perovskite film was only 18.89%.The results show that the lead iodide located on the surface of perovskite film could inhibit the carrier recombination at the interface in the PSCs and significantly improve the PCE of the PSCs.Compared with the traditional way of adding excessive lead iodide into the perovskite precursor solution,the laser-induced self decomposition of triple cation perovskite film to produce lead iodide is easier to control the position and content of lead iodide.(4)Though poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)has been widely adopted as HTM in flexible PSCs,arising from high optical transparency,good mechanical flexibility,and high thermal stability,its inherent acidity and hygroscopicity would inevitably hamper the long-term stability of the PSCs and its energy level does not match well with that of perovskite materials which would lead to a relatively low open-circuit voltage.P-type delafossite CuCrO2 nanoparticles synthesized through hydrothermal method have been investigated as an alternative HTM for[(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08 based inverted architecture PSCs.The average open-circuit voltage of PSCs has increased from 908 mV of the devices with PEDOT:PSS HTM to 1020 mV of the devices with CuCrO2 HTM.Ultraviolet photoemission spectroscopy measurement demonstrated the energy band alignment between CuCrO2 and perovskite was better than that between PEDOT:PSS and perovskite,the electrochemical impedance spectroscopy indicated that CuCrO2 based PSCs exhibited larger recombination resistance and longer charge carrier lifetime,which contributed to the high open-circuit voltage of CuCrO2 HTM based PSCs.