Active Layer Morphology Control And Electron Transport Layer Optimization Of Organic Solar Cells

Organic photovoltaic?OPV? is considered to be one of the most promising green energy technologies,owing to its many advantages such as light weight,simple preparation process,good flexibility,and large-area printing production.The urgent problem in this field is how to improve the power conversion efficiency?PCE?of OPV,and optimizing the active layer and the interface layer is the key to improving the performance of organic solar cells.In order to improve the PCE of organic solar cells,this thesis focuses on studying the effect of high crystalline small molecule manipulates polymer/fullerene morphology,the relationship between the molecular structure of naphthalimide polymer acceptor materials and photovoltaic performance,the influence of SnO₂ electron transport layer?ETL?thickness and morphology on the photovoltaic performance of the device.The main contents were divided into the following three chapters.?1?Study on the morphology of the active layer of polymer/fullerene organic solar cells controlled by highly crystalline small moleculesIn order to improve the film morphology of the active layer of organic solar cells,two high crystalline small molecules?ITDCN/ITDCF?were employed as the third component for PBDB-T/PC₇₁BM system.The improved charge carrier mobility and more balanced?_e/?_h ratio is achieved at a weight ratio of 0.85:0.15:1 for PBDBT:ITDCN:PC₇₁BM ternary system,a weight ratio of0.80:0.20:1 for PBDBT:ITDCF:PC₇₁BM ternary system with?_e/?_h ratio of 1.09 and 1.14,respectively.With increase of ITDCN/ITDCF versus PBDB-T from 5%to 30%,The best average PCE was obtained at the weight ratio of 0.85:0.15:1 for PBDBT:ITDCN:PC₇₁BM ternary system,and the champion device achieved 6.68%PCE with J_SC of 12.78 m A·cm^-2,V_OC of 0.83 V and FF of 0.63,which is 24%higher than binary device.Atomic Force Microscope?AFM?and Transmission Electron Microscope?TEM?characterization demonstrate introducing high crystalline small molecule into polymer/fullerene system is a promising strategy to optimize absorber film morphology and improve device photovoltaic performance.?2?Synthesis of naphthalimide polymer acceptor materials and the study on their photovoltaic propertiesAmong the many polymer acceptor materials,naphthalimide?NDI?polymers behaves high electron mobility,great polarity,low electron cloud density and good stability,due to the larger conjugated framework and strong electron-withdrawing ability,thus showing good photovoltaic performance.In this work,a polymer?PNDIS-HD-OMe?was synthesized using methoxy instead of selenium as the electron-donating unit to improve its HOMO,reduce its band gap,and broaden its absorption.Selenophene is connected to two methoxy groups,which increases the steric hindrance,reduces the reactivity and molecular weight,resulting in a low mobility,making the device based on PCE-10:PNDIS-HD-OMe achieved 1.96%PCE,the device based on PCE-10:PNDIS-HD-OMe:PC₇₁BM achieved 2.98%PCE due to the complementary absorption of PCE-10,PNDIS-HD-OMe and PC₇₁BM.?3?Preparation and optimization of SnO₂ ETLZnO is generally used as the ETL material in invertedOPV.Its intrinsic defects on the surface can easily lead to serious recombination of electrons and holes,which will reduce the electron transfer efficiency and affect the collection of electron by the cathode,though the transition metal oxide?ZnO? has a strong ability to block holes.SnO₂ is an ideal ETL material because of its advantages of high electron mobility,wide band gap,high transmittance,stable chemical properties,and simple preparation process.However,there is no efficient report onOPV using SnO₂ as ETL which is widely used in the field of perovskite solar cells.In this paper,the SnO₂ ETL was first prepared by spin-coating solution on the ITO substrate.However,it is difficult to remove the Cl^-that is derived from the raw material in the solution.In order to eliminate the Cl^- in the solution,SnO₂ was prepared by powder calcination process to prepare SnO₂ ETL.Finally,SnO₂ ETL with good light transmittance is obtained by diluting and spin-coating Tin?IV?oxide on the ITO substrate.SnO₂ and ZnO were used as ETL to prepareOPV devices with P3HT as the donor and PC₇₁BM as the acceptor.When the ETL is SnO₂,the device based on P3HT:PC₇₁BM achieved 2.41%PCE.When the ETL is ZnO,the the device based on P3HT:PC₇₁BM achieved 2.24% PCE.The thin films treated with ZnO and SnO₂ showed similar surface morphology,and the root mean square?RMS?values of the surface roughness were 5.54 and 1.35 nm,respectively.The phase separation of SnO₂ film is more obvious,which is helpful to improve the dissociation of excitons and the charge transfer efficiency,thereby improving the efficiency of FF and devices.Therefore,photovoltaic devices with SnO₂ as the ETL have higher PCE.