Microwave-assisted solvent vapor annealing to rapidly achieve enhanced performance of organic photovoltaics

Abstract

Microwave-assisted solvent vapor annealing (MWSA) treatment is suggested to rapidly achieve high performance organic photovoltaics. Once vaporized polarized molecules are smeared onto an active layer, they are made to oscillate in the active layer remotely by microwaves, which eventually results in the dissipation of heat in the layer. MWSA treatment is analogous to conventional solvent vapor annealing, but the oscillation of polarized molecules with microwave facilitates morphology regeneration in a short time. In this method, vertically favorable segregation of donors and accepters can be achieved due to molecular diffusion of the fullerene-derivative toward the top of the active layer where there exist vacancies between polymer crystallites. This segregation facilitates the charge transport and increases the short circuit current density. Also, the volumetric heat generation by penetrated vapor molecules through oscillation in the active layer induces polymer crystallization and diffusion of fullerene-derivatives. Films treated by MWSA for 7 seconds showed 18% higher power conversion efficiency than pre-thermally annealed films.