The Research On Absorption Layer Optimization And Electron Transporting Layer Modification Of Planar Heterojunction Perovskite Solar Cells

In the past decade,the power conversion efficiency（PCE）of perovskite solar cells（PSCs）has increased from 3.8%reported by Miyasaka et al.in 2009 to the state-of-the-art 25.7%,which has surpassed commercial multicrystalline silicon solar cells and CIGS solar cells.Compared with other structural perovskite cells,planar heterojunction（PHJ）PSCs are more attractive for commercialization due to their high efficiency and simple structure.People need to consider many issues on the road to commercialization of perovskite solar cells,such as device cost,stability,efficiency,repeatability and environmental friendliness.This thesis starts with PHJ PSCs,and improves PSCs from two aspects:optimizing the perovskite light absorption layer and modifying the Sn O₂electron transport layer（ETL）,so as to improve the PCE of the device and ensure the stability of the device.The main research contents are as follows:Firstly,a small amount of guanidine isothiocyanate（Gua SCN）was used as an additive in the process of preparing perovskite thin films by the two-step method,and high efficiency and stablity PSCs were fabricated by regulating the concentration of Gua SCN.The introduction of a trace amount of Gua⁺can strengthen the black phase structure of perovskite by coordinate with[Pb I₆]^4-regular octahedra,resulting in better crystallinity and higher stablity perovskite films.Moreover,the trap-state density in the perovskite film is obviously reduced and the carrier lifetime is remarkably improved after adding an appropriate amount of Gua SCN.In result,when the concentration of Gua SCN additive was 0.5 mg/m L,the average PCE of the PSCs reached 18.89%,and the best device achieved a champion PCE of 20.18%.In addition,the modified PSCs exhibit a good stability.The unencapsulated device remain above 95%of the initial efficiency after being stored in ambient air with a humidity of～15%and temperature of～15℃for 30 days,and the unencapsulated device achieved a steady PCE under continuous illumination for 1000 s.Secondly,based on the first work,the effects of four guanidine salt additives with different anionic on PSCs were investigated.They are Gua SCN,guanidine hydrochloride（Gua Cl）,guanidine hydrobromide（Gua Br）and guanidine hydroiodide（Gua I）.After characterizing the morphology,crystallinity,carrier lifetime and trap-state density of perovskite films prepared with different guanidine salts,the photovoltaic parameters of PSCs fabrication with different guanidine salts were measured.In result,it was found that when the anion is a volatile ion（Cl^-,SCN^-）,the guanidine salt additive has a higher performance improvement for PSCs.Among them,the PSCs modified with Gua Cl have the best comprehensive photovoltaic performance and achieve a highest PCE of 20.39%with hardly hysteresis.Then,a 3-mercaptopropyltrimethoxysilane（MPTMS）Self-assemble monolayer（SAM）is employed as an modified layer on the surface of Sn O₂ ETL.Due to its smooth surface and the coordination of sulfhydryl functional groups with Pb I₂,this MPTMS-SAM can increase the grain size of the perovskite film and improve the quality of the perovskite film.On the other hand,it can enhance the charge extraction capability of the ETL and thus improve the carrier dynamics in the whole device.In result,with MPTMS SAM modification,the average PCE of the PSCs is significantly improved from 16.62%to 18.75%,and the best device achieved a champion PCE over 20%with little hysteresis.Moreover,the modified PSCs exhibit excellent stability.Finally,we investigated the performance of three Sn O₂ ETLs.They are Sn O₂colloid film（C-Sn O₂）prepared with Sn O₂ colloid solution as precursor solution,Sn O₂quantum dot film（Q-Sn O₂）prepared with Sn Cl₂solution as precursor solution,and Sn O₂ bilayer film（B-Sn O₂）prepared by modifying Sn O₂ quantum dot on the surface of C-Sn O₂.The surface morphology,roughness,light transmittance,charge extraction ability of three ETLs as well as quality of the perovskite films prepared on their surfaces were characterized.In result,by comparing the photovoltaic parameters of the three devices,it is found that modifying Sn O₂ quantum dots on the surface of C-Sn O₂ can effectively improve the open circuit voltage and fill factor of the PSC,thereby improving the efficiency of the device.