Ultrasonic spray coating of 6.5% efficient diketopyrrolopyrrole-based organic photovoltaics

Ultrasonic spray coating was tailored for the deposition of diketopyrrolopyrrole-based polymer: fullerene films. Concurrently pumped spray coating was used to rapidly and precisely sweep photoactive layer thickness and donor:acceptor ratio. The highest reported efficiency for a spray-coated device of 6.5% was achieved and verified by external quantum efficiency. The short-circuit current density of the complete device stack was optically simulated as a function of thickness, agreeing with experimentally measured device performance. Charge carrier mobilities were studied as a function of fullerene loading, suggesting electron mobility limited performance. This paper shows that implementing the industrially relevant deposition technique of spray coating results in no performance loss relative to lab-based spin coating.