A morphology study on sprayed thin films for high performance and air-stable organic solar cells

Abstract

High efficiency and air-stable of bulk heterojunction (BHJ) structured organic solar cells (OSCs) were fabricated using a gas-assisted spray (g-spray) method that can be adapted to large-scale high-throughput continuous production. A facile and effective external treatment method for controlling the morphology of BHJ-OSCs using a g-spray technique was demonstrated. The bulk film morphology and internal nanomorphology of the active layers were well manipulated using a sprayed solvent overlayer (SSO) treatment. The efficient nanomorphology evolution which is a prerequisite for obtaining high performance of OSCs could be realized by SSO. The SSO treatment was a simple and rapid process that could be carried out at room temperature, unlike conventional external treatment methods such as solvent- or thermal-assisted treatment. In addition, the SSO treatment is a practical method to improve the performance of polymer based organic thin film transistors (OTFTs). After sprayed P3HT active layers were subjected to SSO treatment, the charge mobility of the devices was enhanced by an order of magnitude as a result of preferential chain re-arrangement. Even though the as-sprayed P3HT active layer has a low crystallinity without a particular chain ordering due to the rapid drying of solvent during film formation, SSO treatment can re-arrange the P3HT chains into the preferentially edge-on orientation. The orientation direction of P3HT was controlled to be an edge-on dominant orientation that is preferential for charge transport after SSO treatment. Finally, based on the skill of optimizing photoactive layers via spray technique, high performance air-stable full sprayed OSCs were demonstrate. Sol-gel derived ZnO solution was employed to an electron-transporting layer (ETL) because sol-gel method is really suited to the solution process. ZnO crystalline has an anisotropy charge transport direction depending on crystal growth direction which varied with the thermal annealing...