Research of Electrode Modification for Organic Solar Cells
|School||Dalian University of Technology|
|Course||Microelectronics and Solid State Electronics|
|Keywords||organic solar cell inverted architecture charge transport Cul molecularorientation|
Organic solar cells have attracted considerable interest and investigation due to their potential for low-cost, light-weight and flexible applications. However, because the photoelectric conversion efficiency (PCE) is still low compared with silicon-based solar cells and the physical mechanism is still unknown, organic solar cells have been unable to use in commercial applications nowadays. Considering of the progress of current research and laboratory conditions, in this thesis we did the following investigation.Firstly, we introduced ZnO and MoO3to modify the cathode and anode, respectively. The device structure and process based on P3HT:PCBM were optimized. The results showed that annealing had a great effect on the performance of the device. The best annealing condition for P3HT:PCBM layer was160℃for30min under the environment of nitrogen. Contrasting the four different cells include the normal cells and inverted cells, we found that the inverted device had shown better performance. The device of ITO/ZnO/P3HT:PCBM/Mo03(10nm)/Al (70nm) had a photoelectric conversion efficiency of2.9%. By investigating current-voltage (I-V) characteristics of the single carrier device based on P3HT:PCBM, we found that in P3HT.PCBM mix layer, the main charge carrier was hole.Secondly, we investigated the charge transport of the organic solar cell with an inverted architecture. The ideality factor value (1.55) was higher than unity for the organic solar cell, which indicated the presence of the non-deal behavior. In this structure, deposition of organic semiconductor on to the inorganic semiconductor can generate a large number of interface states at the semiconductor surface. The barrier height value obtained from C-V measurement was higher than that obtained from I-V measurement due to the interfacial organic layer, the interface states and the barrier inhomogeneity of the device. The ideality factor n, open circuit voltage Voc, short circuit current density Jsc, fill factor FF, PCE and Richardson constant A*values for the organic solar cell were found to be1.63,0.57V,8.2mA/cm2,61%,2.9%and7.41A/cm2K2, respectively.At last, we studied the organic solar cell using a CuI buffer to control the molecular orientation and modify the anode. By introducing a CuI buffer between indium tin oxide (ITO) and CuPc, the power conversion efficiency was significantly enhanced by a factor of-70%to2.55%. Because of the strong interactions between the CuI and CuPc, the stacking orientation of CuPc molecules was changed, resulting in a～65%increase in absorption coefficient, a larger carrier mobility and a smoother film surface. Through XPS and UPS, we found that the anode work function was raised by the formation of a dipole layer between ITO/CuI interfaces.