Photovoltaic Devices Research Based On Deep-Level Polymer Electron Donor Materials And Non-Fullerene Electron Acceptors

The increasingly serious energy and environmental problems have aroused widespread concern in all sectors of society,and the solar cells which convert green solar energy directly into electrical energy have become a research craze.Polymer solar cells have become the mainstream in the field of solar cell research because they overcome the defects of traditional inorganic solar cell,such as high production cost,difficult to process and so on,but possess the advantages of easy processing,light quality and low cost.In recent years,non-fullerene small molecular acceptors are widely applied in the field of polymer solar cells to overcome the limited absorptive region and fixed-energy-level drawbacks of fullerene-based acceptors.Up to date,the energy conversion efficiency of tandem photovoltaic cells constructed with polymer donor materials and non-fullerene acceptors has reached to 17%.In view of the important role of band gaps and molecular energy levels in polymer solar cells,this thesis focuses on the study of polymer solar cells based on deep energylevel polymer electron-donor materials and non-fullerene electon-acceptor materials,to achieve enhanced performance in polymer solar cells.There are four chapters in the thesis,the first chapter summarizes the research background of polymer solar cells,working principle of cells,photovoltaic materials,device structure and device performance optimization and so on.The second chapter mainly introduces the device preparation and a number of performance testing methods.In the third chapter,a fluoroquinoxaline-based deep energy level polymer poly{4,8-di(2,3-dioctylthiophene-5-yl)-2,6-benzo[1,2-b:4,5-b’]dithiophene-alt-5,5-[5’,8’-di-2-t hienyl-(6’-fluoro-2’,3’-bis-(3’’-octyloxyphenyl)-quinoxaline)]}(PBDTT-FTQ-DO)is used as the electron donor material to blend with three non-fullerenes small molecular acceptor material with similar structures(ITIC,ITIC-Th and ITIC-Th1).Effects of side-chain and end-group modifications of the non-fullerene acceptors on the photovoltaic performances of corresponding devices were systematically studied.The energy conversion efficiencies of the three system devices were obatianed as 2.85% for ITIC,7.81% for ITIC-Th and 6.92% for ITIC-Th1-based devices,respectively.To illustrate the physical mechanism of the performance diffenerces in the three acceptors-based devices,charge transfer,absorption spectra and morphology invetaigations were performed in detail.In the fourth chapter,to further optimize the device performance and obtain higher photoelectric conversion efficiency,a new chlorinated wide band gap polymer donor(J52-2Cl)and a main chain twisted A-D-A type non-fullerene acceptor i-IEICO-4F were selected to fabaricat polymer solar cell.A high efficiency value of 13.16% was obtained after thermal annealing at 170 °C for 10 min,which is one of the highest results of J52-2Cl-based PSCs.The mechanism of performance improvement in J52-2Cl and i-IEICO-4F system was described by studying the film absorption,exciton resolution rate and carrier mobility before and after thermal annealing treatment.