Efficient Flexible Organic Solar Cells with a Low-Temperature-Processed Al-Doped Zinc Oxide Electron Transport Layer
Jubin Jang, Ju‐Hyeon Kim, Sanseong Lee, Chang‐Mok Oh, In‐Wook Hwang, Seungchan Kim, Aeri Park, Dong Hyun Kang, Chelim Jang, Taeyoon Ki, Heejoo Kim, Kwanghee Lee
Abstract
Zinc oxide (ZnO) has been widely used in inverted organic solar cells (I-OSCs) as the electron transport layer (ETL) due to its excellent electrical properties. However, the high-temperature process (>300 °C) applied to the ZnO ETL to enhance its electrical properties has been regarded as the bottleneck for application of this ETL to flexible I-OSCs due to the limited temperature tolerance of flexible substrates. In this work, we synthesized aluminum (Al)-doped ZnO with a sol–gel process (AZO) and successfully demonstrated highly efficient flexible I-OSCs with a low-temperature-processed (140 °C) AZO ETL (AZO 140 °C). Since Al doping of ZnO results in an enhanced electrical conductivity and reduced defects in ZnO even for low-temperature-treated materials, the rigid and flexible I-OSCs with AZO 140 °C ETLs exhibit power conversion efficiencies (PCEs) of 16.3 and 14.4%, respectively, which are higher than those of I-OSCs with low-temperature-processed (140 °C) ZnO ETLs. Furthermore, the unencapsulated I-OSC with the AZO ETL exhibits improved storage stability ( T 80 > 5000 h) compared to that with the ZnO ETL ( T 80 = 100 h), and an excellent thickness-insensitive PCE is also obtained for the I-OSCs with various thicknesses of the AZO ETL (22–190 nm). These results provide meaningful insight into reducing the process temperature of an ETL toward high-performance, flexible electronic systems.