Solid additive-assisted morphology optimization enables efficient nonhalogen solvent-processed polymer solar cells

Abstract

Controlling and optimizing the photoactive layer morphology is closely related to the process of exciton dissociation, charge transfer and collection and thus is crucial for building a high-performance polymer solar cell (PSC). Due to the limited solubility of non-halogenated solvents and the strong crystallinity of Y6 acceptors, it is a challenge to optimize the morphology of the Y6-based blend active layer processed by a non-halogenated solvent for achieving a high photovoltaic performance. In this work, we develop a morphology controlling method by applying BTBT and DTBDT as solid additives to regulate the phase separation of the o-xylene-processed PM6:Y6 blend films. The strong crystalline behavior of BTBT and DTBDT can restrict the over-aggregation of Y6 molecules in a low volatility processing solvent during the film formation. The stronger crystallinity and better miscibility with Y6 of BTBT over DTBDT lead to a favorable effect in facilitating the formation of a nanoscale bicontinuous interpenetrating network in the PM6:Y6 active layer. As a result, the o-xylene-processed PM6:Y6-based PSC treated with BTBT and DTBDT additives shows an enhanced power-conversion efficiency (PCE) of 16.37% and 14.40%, respectively, as compared to the control device (PCE = 10.25%) using 1-chloronaphthalene as a solvent additive.