Research On The Bulk Heterojunction Organic Photovoltaic Solar Cell Based On Ternary Active Materials

Organic photovoltaic cells are attracting great attention due to their low cost, easy fabrication, light weight, flexible, and etc. In recent years, great improvement has been achieved in the device performance of the organic photovoltaic cells; the power conversion efficiency of the photovoltaic devices based on the bulk heterojunction (BHJ) structure has achieved 5-6%. Whereas in the common two component BHJ photovoltaic cells, because the donor polymer and the acceptor materials are not spacially separated, the charge recombination is very great, resulting in a very low exciton diffusion efficiency (<10%). Therefore, the power conversion efficiency is largely restricted. In this article, ternary active layer based polymer photovoltaic cells were designed and fabricated, the charge recombination efficiency is largely restricted and the whole device performance is greatly improved. The ternary active layer contains a polymer donor material, an acceptor material, and a hole transport mateial. The highest occupied molecular orbital (HOMO) level of the hole transport material is relatively higher than that of the polymer donor material. In the active layer, the polymer donor material is the majorest component, while the acceptor material and the hole transport material is the minor components. The phase separation occurs among the three components because of their thermodynamically immisability. The accepor material and the hole transport material disperse in the donor materials phase and therefore separated from each other by the donor material. The electron acceptor material serves as the electron transport pathway, and the hole transport material serves as the hole transport material because of the relatively lower HOMO level compared to that of the donor material. Therefore, the electron transport pathway is spatially separated from the hole transport pathway and the recombination of the positive and negative charge carriers are effectively retarded. Therefore, the whole performance of the photovoltaic devices is greatly enhanced. We fabricated ternary component BHJ photovoltaic device based on PPE/PVK/C60, PPE/TPD/C₆₀, and PPE/TPD/SWNTs.Compared with the traditional two component BHJ photovoltaic devices based on PPE/C₆₀, PPE/C₆₀, and PPE/SWNTs, the powerconversion efficiency is increased by almost 1 order of magnitude.