Improving The Photoelectric Conversion Efficiency Of Organic Solar Cells By O₂Doping And Interface Modification

Energy is the motive of social development, and offers livelihood protection to human beings. Nowadays, the rapid growth of energy demand and consumption follows the fast development of economy. Many countries even started wars to others just for energy. Apparently, energy has been a major problem in the world, and it’s important to find alternative and renewable resources. Solar energy is an excellent choice and more and more researchers pay their attentions to the exploitation and optimization of solar cells. In this paper, in order to improve the photoelectric conversion efficiency of organic solar cells (OSCs) based on CuPc/C60, we did three different experiments, including active layer doping, structure optimization and electrode modification.To begin with, an improvement of photovoltaic characteristics has been demonstrated in heterojunction organic solar cells (OSCs) with an ITO/(CuPc)/C60/Alq3/Al configuration by doping O2into the donor layer. After the O2adsorption, electrons are transferred from the CuPc ring to the adsorbed acceptor gas O2and the holes residing in the film are delocalized, the presence of h+and O2-species on the film surface can be connected with a shift of the Fermi level position, which causes a band-bending. With O2doping into CuPc, both the short-circuit current and open-circuit voltage are changed remarkably, the power conversion efficiency increases by25%compared to that of the organic photovoltaic cell with only CuPc.What’s more, organic solar cells with an inverted architecture were investigated. And in order to improve the performance of these C6o/CuPc based cells, some measures were taken to improve the ability of transporting and collecting charge carriers. Firstly, we optimized the thickness of MoO3and BCP, which were used to transport holes and block excitons. Secondly, we used Cul to modify ITO, and then treated them by ammonia plasma. The results show that these methods are helpful and some measurements could help to explain the reasons. Some tests were taken to tell the difference between ITO/Cul film who were treated by ammonia plasma or not. Finally we come to a conclusion that the ammonia plasma treatment could change the work function, as well as form a new material which will help to extract and transport charge carriers.Finally, a method of improving photovoltaic characteristics was researched in organic solar cells with an ITO/CuPc/C60/BCP/LiF/Al configuration by ammonia plasma treating ITO and inserting MoO3between ITO/CuPc. The work function of ITO can be increased by ammonia plasma treatment, and with the inserting of MoO3buffer layer, the energy barrier of holes transporting was decreased. The electrical characteristics of OSCs with twice ammonia plasma treating ITO (before and after the deposition of MoO3) were studied, and the results showed that the power conversion efficiency was increased significantly. The improvement can be attributed to the ohmic contact which was a result of the new energy band changes of anode ITO, and it is beneficial to the extraction and collection of holes.