Fabrication And Performance Research Of High Open-circuit Voltage Polymer Solar Cells

Today,with the rapid development of science and technology,the energy problem has become the most crucial problem of our people.To develop a clean and efficient energy is the key to solve the energy problem.In the past decades of exploration,solar cell technology that can directly convert solar energy into electricity has proved to be an important solution to the energy crisis.In numerous researches of solar cell,with the advantages of low cost,easy processing,light weight and flexibility organic solar cell has attracted extensive attention.Although organic solar cell has unique potential,there are several key issues still remain before they can be commercialized on a large scale.One of the most urgent one is how to achieve breakthrough on its power conversion efficiency（PCE）.As known to all,among several factors that affect the PCE of organic solar cell,open circuit voltage(V_oc) always show the most direct influence on PCE.Hence,making organic solar cells with high V_oc is an important direction to realized breakthrough in its PCE.Thus these polymers have great potential on organic solar cell application.Our researches are focused on organic solar cells with high V_oc based on different kinds of polymer.In chapter 2,a new polymer donor based on 3,3’-difluoro-2,2’-bithiophene（2F2T）and difluorobenzoxadiazole（ffBX）,named 2F2T-ffBX is designed and synthesized.The organic solar cell（OSC） based on 2F2T-ffBX donor and [6,6]-phenyl-C60-butyl acid methyl ester(PC₆₁BM) acceptor exhibits a high efficiency of 7.3% with a high open-circuit voltage(V_oc) of1.03 V.When blended with perylenediimide-based acceptor（PDI6）,the corresponding OSC shows a higher V_oc of 1.19 V with a low energy loss of 0.50 eV but a much lower efficiency of 2.0%.The detailed analyses including charge generation,transport,recombination properties,and morphology were performed to understand the performance of corresponding devices.In chapter 3,we fabricated BHJ solar cells with two different low HOMO conjugated polymer donor containing B-N covalent bond called PBN2T and PBN2F2T alongside with two acceptors PC₆₁ BM and EH-IDTBR.These four devices achieved PCE of 3.5%、5.1%、4.1% and 1.9%respectively.Then,the further investigation of the device performances shows that the low electron mobility and significant charge recombination hinder the device performance.From these results we found that although introduced F atoms can adjust the energy of a material to obtain deeper HOMO energy levels of polymer material,which makes it have a higher open circuit voltage devices.,but it will also reduce the solubility of material,thus affecting the film-forming processing process and the formation of different nanometer microstructure,which might cause lower charge transfer mobilities.Therefore,simply introducing F atom to adjust the structure and energy level of the material cannot directly improve the photovoltaic performance of the organic solar cellIn chapter 4,we used three similar donor materials J52,J52-F and J52-FS with decreasing HOMO to blend with polymer acceptor material NOE10 to fabricate organic solar cells for exploring the application of deep HOMO level conjugated polymers in all-polymer organic solar cells.After a series of optimization of processing conditions,the PCE of the three groups of cell devices was achieved at 7.5%,8.3% and 3.8%respectively,with the open circuit voltage of 0.79 V,0.90 V and 0.93 V.We further investigate the charge generation,transmission,recombination performance of three devices as well as the morphology of the blend film.Meanwhile,resonant soft X-ray scattering（R-SoXS）was introduced to analyze the differences of three active layers’size distributions.After a series of characterization and analysis,we found that the active layer of F52-FS:NOE10 has bimodal size distribution with lowest volume fraction of the smaller domains,which led to the serious bimolecular compound process,making its efficiency lower than that of the other two groups of devices.It can be seen that polymer materials with deep HOMO level have wide applications in all-polymer organic solar cell systems due to the high open circuit voltage they provide.