Design And Synthesis Of Simple Polymer Donor And Unfused-Ring Acceptor Materials And Their Application In Organic Solar Cells

Organic solar cells（OSCs）have attracted widespread attention due to their unique advantages such as light weight,solution-processability,flexibility,semitransparent and large-area fabrication.At present,organic solar cells are still difficult to meet the requirements of commercial application because of the limited variety of high-performance donor and acceptor materials and the complex structure and high synthesis cost.This thesis is mainly based on the understanding of the relationship between the molecular structure and photovoltaic performance of organic solar cell active layer materials.Around the simple structure,low-cost and high efficiency polymer donor and unfused-ring acceptor materials of light absorption,energy level regulation,and active layer morphology optimization.A series of thiophene-vinyl-thiophene polymer donors and unfused-ring acceptor materials based on simple structure,low cost,and easy synthesis were designed and synthesized,and applied to high-efficiency organic solar cells.The specific research contents and results are as follows:1.Two novel A₁-A₂ type wide bandgap copolymer donors,PV2TC-BDD and PV2TC-FTAZ,were designed and synthesized by a new acceptor unit A₁,2-butyl-1-octyl carboxylate substituted thiophene-vinyl-thiophene（V2TC）with two different acceptor units A₂,benzo-[1,2-c:4,5-c′]dithiophene-4,8-dione（BDD）and difluorobenzo[d][1,2,3]triazole（FTAZ）,respectively.The small and simple vinyl unit can effectively reduce the steric hindrance and improve the planarity of molecules,deepen the highest occupied molecular orbital（HOMO）level,enhance the light absorption and facilitate charge transport.The two copolymer donors show a deep-lying HOMO level of-5.50 e V for PV2TC-BDD and-5.35 e V for PV2TC-FTAZ.The absorption bands of the copolymers are observed to distinctly red-shift than those of the reported A₁-A₂ type copolymers based on carboxylate substituted thiophene.As a result,when blended with IT-4F,both of A₁-A₂ type copolymers obtain an improved short-circuit current density(J_sc)of 18.83 m A cm^-2for PV2TC-BDD and 20.49 m A cm^-2 for PV2TC-FTAZ,which is the highest value for the A₁-A₂ type copolymer-based devices.The PV2TC-BDD-based organic solar cell also achieves a high power conversion efficiency（PCE）of 11.50%,which is an outstanding performance of the devices based on A₁-A₂ type polymers.These results demonstrate that introducing the new acceptor unit V2TC to construct high efficiency A₁-A₂ type copolymers is an effective strategy to develop high performance polymer donors for OSCs.2.A simple donor unit（E）-1,2-bis（3-chloro-5-（trimethylstannyl）thiophen-2-yl）ethene（TVTCl）,was synthesized via side chain chlorination,and a new polymer donor PTVTCl-BDD was obtained by copolymerization with the acceptor unit BDD.Compared with the non-chlorinated polymer PTVT-BDD,the side-chain chlorinated polymer PTVTCl-BDD has a lower HOMO energy level of-5.54 e V,which contributes to higher open-circuit voltage(V_oc).Moreover,PTVTCl-BDD has higher absorption coefficient,stronger crystallinity,and good planarity,which can effectively enhance the light absorption,thus improving the J_sc and device performance.When blended with acceptor Y6,a superior device efficiency of 13.42%was obtained based on the PTVTCl-BDD:Y6 blend film,with a high V_oc of 0.86 V and a high J_sc of 22.71m A cm^-2.In contrast,the lower photovoltaic performance of 7.58%and a lower V_oc of0.76 V based on PTVT-BDD:Y6 blend film.Furthermore,the polymer PTVTCl-BDD has good miscibility with the acceptor Y6,more obvious face-on orientation and tightπ-πstacking,which is beneficial to obtain a good nanofiber morphology,promote charge transport,and improve the device performance.The results show that chlorination strategy is one of the effective methods to design and develop simple,low-cost,high-performance polymer donor materials.3.In order to solve the problem of low V_oc and moderate fill factor（FF）of current unfused-ring acceptors（UFAs）,two novel A-D-A′-D-A type unfused-ring acceptors BTCD-IC and BTCD-2FIC,which have the same electron-withdrawing central-core dithieno[3′,2′:3,4;2′′,3′′:5,6]-benzo[1,2-c][1,2,5]-thiadia-zole（DTBT）and cyclopentadithiophene unit（CPDT,substituted by 2-butyl-1-octyl alkyl chain）coupling with different terminals 3-（dicyanomethylidene）indan-1-one（IC）and2-（5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene）malononitrile（2FIC）,were designed and synthesized.Two UFAs showed strong and broad light absorption in the wavelength range of 300-850 nm owing to the strong intramolecular charge transfer effect favorable by DTBT core.Compared with BTCD-IC,BTCD-2FIC with F-containing terminal group exhibited higher molar extinction coefficient,lower energy level,higher charge mobility,stronger crystallinity,more ordered molecular stacking,and better film morphology.As a result,when blended with donor polymer PBDB-T,the BTCD-2FIC-based device achieved a superior power conversion efficiency（PCE）of 11.32%,with a high V_oc of 0.85 V,a J_sc of 18.24 m A cm^-2 and a FF of 73%,than BTCD-IC-based device（PCE=8.96%）.Impressively,the simultaneously enhanced V_oc and FF values of the PBDB-T:BTCD-2FIC device were the highest values of the A-D-A′-D-A type UFAs.The results demonstrate the application of electron-withdrawing DTBT central-core unit in efficient UFAs provides meaningful molecular design guidance for high-performance organic solar cells.