Improved performance in organic solar cells using aluminum-doped cathode-modifying layer

Organic solar cells (OSCs) have been developed using aluminum-doped bathocuproine (BCP:Al) as cathode-modifying layer. Although BCP:Al thin film shows decreased electron mobility than neat BCP thin film, the former is advantageous over the latter in the following two aspects. Firstly, BCP:Al has more gap states, offering more efficient electron injection and extraction at the interface with electron acceptor, thereby contributing to the increase in fill factor. Secondly, BCP:Al increases the optical absorption of device, contributing to the increase in short-circuit current density. As a result, the OSC based on BCP:Al shows improved power conversion efficiency than that based on neat BCP. Moreover, the former device presents increased thermal stability than the latter, mostly because doped Al clusters can inhibit the aggregation tendency of BCP molecules. We provide a novel insight to fabricate cost-effective cathode-modifying layers, useful for pushing forward the commercialization of OSCs.