Polymer Solar Cells Based On Narrow Band Gap Polymers With BDT Group

ABSTRACT:With the development of social economy, non-renewable resources gradually exhausted. At the same time,the energy of the irrational exploitation and utilization has also brought serious environmental problems. To achieve the strategic objectives of sustainable development, we must rely on scientific and technological progress, and the development and utilization of renewable energy for the positive, such as water, wind, and solar energy. Thesolar energy has great potential, which is rich in the earth.The solar cells haveattracted more and more attention as one of the main research goal of clean and renewable energy. In recent years, the rapid development of conducting polymer makes the development of low cost organic solar cells as possible. Conjugate conducting polymers have polymer workability and flexibility as well as inorganic semiconductor or metallic conductivity and thus has great potential commercial value. This paper mainly studies solar cells based onthe BDT narrowband polymers by using optimization methods for anode buffer layer and using multiple solvent and solvent annealing to improve the energy conversion efficiency of the devices.A series of polymer solar cells (PSCs) based on poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b’(dithiophene)-2,6-diyl-alt-(4-(2-ethyl hexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl](PBDTTT-C) and [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) were fabricated with various anode buffer layers. The power conversion efficiency (PCE) of PSCs was improved to4.91%for the cells with PEDOT:PSS/LiF(1nm) as anode buffer layer, which corresponds to26.2%efficiency improvement compared with the cells with PEDOT:PSS as anode buffer layer. The PSCs with PEDOT:PSS/LiF as anode buffer layer shows a maximum short circuit density (Jsc) of13.70mA/cm2, with open circuit voltage (Voc) of0.73V and fill factor (FF) of49.1%under illumination100mW/cm2AM1.5G simulated solar light. The dominant mechanism for the performance improvement of PSCs could be attributed to the increased charge carrier collection ability by anode buffer layers.A series of high performance of polymer solar cells (PSCs) were fabricated with poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b’](dithiophene)-2,6-diyl-alt-(4-(2-ethy lhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl](PBDTTT-EFT) as the donor and with [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor. The PSCs processed with DCB/CBmixed solventsshow an open circuit voltage (Voc) of0.79V, a short circuit current density (Jsc)of13.63mA/cm2and a fill factor (FF) of62.9%, resulting in the highest PCEof6.77%compared with PCE of5.99%for CB as solvent and PCE of5.39%for DCB as solvent. The PCE ofPSCs processed with DCB/CBmixed solvents is further increased to7.58%from6.77%bychloroform vapor annealing treatment for60seconds. The PCE improvement should be attributed to the optimized bi-continuous interpenetrating networks of PBDTTT-EFT:PC71BM for better exciton dissociation and charge carrier collection. This shows the important effect of solvent system of rational choice on the performance of the device, and provides a new way for efficient device optimization.