Novel Optimization Methods For Organic Solar Cell Devices And Effects On Photovoltaic Property

As the problems of energy shortage and environmental pollution become all the more imperative, the demands for new alternative energy sources increased rapidly posing a big challenge for all human kind in the 21th century. Solar energy is supposed to be one kind of clean energy source that is available almost all the time paving a promising way for solving the energy and environmental problems. Polymer solar cells (PSCs) are getting growing attention due to their advantage of light weight, cost-effective and ability to be fabricated into large-area flexible devices. In this dissertation, we mainly focus on optimizing photovoltaic performance based on new donor materials and developing and investigating novel methods to improve the photovoltaic property of PSCs. The main results are summarized as follows.1. Employing self-synthesized D-?-A-?-A structured polymer materials PC-TBTBT as electron donor and fullerene derivative [6,6]-phenyl C71-butyric acid methyl ester (PG71BM) as electron acceptor, devices with the configuration of ITO/PEDOT:PSS/Polymer:PC71BM/Ca/Al were fabricated. Through a series of optimizing processes such as controlling D/A ratio, solution concentration, solvents, additives, thermal annealing and methanol treatment, the power conversion efficiency (PCE) based on PC-TBTBT: PC71BM reached 4.74%, with Voc= 0.99 V, Jsc= 9.70 mA/cm2, and FF= 0.48 under illumination of AM1.5G,100 mW/cm2, greatly higher than the control device based on D-?-A structured polymer PC-TBT (PCE= 4.05%). The impacts on photovoltaic properties were further studied in terms of external quantum efficiency (EQE), charge carrier mobility and film morphology.2. Post-modification of PEDOT:PSS with dimethylsulfoxide (DMSO) solvent was reported, through which the efficiency based on poly [N-9"]-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',l',3'-benzot hiadiazole) (PCDTBT):PC71BM PSC increased by 10% to 6.52%, with simultaneous increase in Jsc and FF. To investigate the mechanism of this treatment, chemical element, impedance resistance and charge carrier mobility were studied.3. Two high boiling point solvents namely DMSO and diphenylether (DPE) were employed as co-additives in fabricating PCDTBT:PC71BM PSCs. It was found that the PCE can be improved to 7.13% for the PSCs processed with co-additives in comparison with ?6.5% for the PSCs processed with either DPE or DMSO additives. We also investigated the effects of the co-additives systematically.