Research Of Polymer Solar Cells Based On P3HT: PCBM

Recent years, organic solar cells have attracted much attention due to its unique advantages such as flexible, lightweight, low cost and large-area devices. In early April, 2011, Mitsubishi Chemical and university of Tokyo reportedly set a new efficiency record, producing organic solar cells with a 9.2% power conversion efficiency (PCE) that broke the limit of commercialization, which brought hope to the people. As an important branch in the field of organic solar cells, polymer solar cells are developing quickly, and have achieved many important results. However, compared to inorganic solar cells with PCE close to 25%, the PCE of organic solar cells, especially polymer solar cells is relatively low, more researches are expected.Polymer/fullerene bulk heterojunction solar cells were investigated as the main subject of this thesis. Researching and analysing of the photoelectric conversion process and the loss mechanism of polymer solar cells, we found that one of the key factors influences on the carrier transport in polymer solar cells is the nano-scale morphology of thin film. Therefore, Our work was focused on the photosensitive layer morphology control. We not only investigated the effect of some effective approaches, such as the selection of solvents, solvent vapour treatment and thermal treat, on the morphology of polymer solar cells, but also optimized the morphology of the photosensitive layer in polymer solar cells and improved the photoelectric conversion efficiency of the devices. We got the main conclusions as follows:â‘ For P3HT:PCBM as the photosensitive layer, the devices prepared with chlorobenzene as the solvent were superior to that prepared with toluene or o-dichlorobenzene as the solvent. AFM diagrams showed that P3HT and PCBM in chlorobenzene as solvent had a suitable phase separation.â‘¡It was demonstrated that optimized post-treatment, such as solvent vapour treat or thermal annealing, forces the P3HT molecules to self-assemble, which induces continuity and correct interpenetrating networks being favorable for electrons and holes transporting and enhancing the power conversion efficiency of the devices.â‘ In addition, for enhancing overlap of the absorption spectra of photosensitive layer with the solar spectrum, we designed a type of polymer solar cells with a structure of ITO/PEDOT:PSS/PbPc/P3HT:PCBM/Al. Lead phthalocyanine (PbPc), which is a p type small molecule material, has a broad and strong absorption in the range from 600 nm to 800 nm, which is complementary with the absorption spectrum of P3HT (400 nm-650 nm). In this thesis, The polymer solar cells with PbPc expended the absorption spectra of devices, but they still need further optimization.