Improved Conversion Efficiency of Organic Solar Cells with CuPc/C60 Heterostructure by Electron Transport Layer

摘要

Organic solar cells (OSCs) have attracted interesting attention due to the properties of low weight on flexible substrates [1], low-cost [2]. Unfortunately, the power conversion efficiency (PCE) of OSCs has been quite poor. Therefore, the improving PCE of OSCs is an important issue. Many researchers improved the OSCs performance, including the introduction of mixed donor-acceptor heterojunctions [3, 4], triplet active materials [5], light-harvesting structures [6], and the electron transport layer (ETL) [7]. For example, Forrest group promote that the improved power conversion efficiency (PCE) of the organic solar cells is due to introduction of bathocuproine as ETL between fullerene (C_(60)) and aluminum (Al) cathode. The authors found that when no ETL material is present, two mechanisms may result in lower efficiency of the devices: (1) During the deposition processing of Al, atoms of Al impact into C_(60) leads to low conductivity of C_(60) [8]. (2) a covalent bond is formed between C6o and Al, resulting in inefficient electron collection between C_(60) and Al [9]. It has become evidence that ETL can improve the PCE of OSCs, but the reasons for this remain unclear. In our work, PBD, Alq_3 and BCP were used as ETL's in photovoltaic devices based on the CuPc/C6o heterojunction. We show that the different PCE of devices with ETL was analyzed in terms of energy diagram level, UV/vis absorption spectra.