The Influence Of The Buffer Layer On The Conventional Organic Polymer Solar Cells

Interface buffer layer is one of the important research contents of each research group. At present, the research contents of this field mainly includes the following two aspects:one is the application of new materials as interface buffer layers, and the other is to simplify the production process and cut down the production cost. Currently, the vacuum vapor deposition, chemical vapor deposition, pulsed laser deposition and the solution process have been applied to fabricating interface buffer layers.Firstly, solution soaking method and vacuum evaporation method were used respectively to the preparation of sodium chloride film as the buffer layer and organic polymer solar cells with structure of ITO/PEDOT:PSS/P3HT:PCBM/NaCl/Al were prepared. At the same time, we prepared devices without cathode modification. The device performance was characterized and analyzed. Through the experiments, We find the device performance has a different degree of increase by the solution soak method and the vacuum evaporation method. Analyzing the experimental data of the two methods, we can see that the devices prepared by the solution soak method have high short circuit current density, but the sharp decline in fill factor and the short circuit current density and the fill factor of the devices prepared by the vacuum evaporation method have obvious ascension. Comparing with the best devices made by the soaking solution method, the power conversion efficiency of the devices prepared by the vacuum evaporation method have been improved 11.9%. So the vacuum evaporation method can replace solution soak method applied in the preparation of organic polymer solar cells.The cesium chloride (CsCl) methanol solution was introduced into the conventional organic polymer solar cells as cathode buffer layer to improve its properties. The charge accumulation between the Al cathode and PTB7 ([poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl])/PC70BM ([6,6]-phenyl C70-butyric acid methyl ester) was analyzed through Capacitance-Voltage (C-V) measurement and the change of work function of Al was investigated by ultraviolet photoelectron spectroscopy (UPS). The results show that the short-circuit current (Jsc), the open-circuit voltage (Voc), the fill factor and the power conversion efficiency (PCE) of the device with the CsCl methanol solution treatment has been improved. And the PCE reaches 6.36%, which has been improved 11% when compared with the methanol treatment devices and 42.6% when compared with the devices without any treatment. This one-step solution treatment can improve the device properties by reducing the charge accumulation and decreasing the work function of Al cathode which is benefit to electron collection.