Orthogonal solvent-sequential deposition of a nonfullerene acceptor solution on polymer donor film: complete interpenetration and highly efficient inverted organic solar cells

Abstract

Sequential deposition (SD) of a nonfullerene acceptor solution on polymer donor film usually results in an active layer with a planar heterojunction or p–i–n heterojunction, which is optimal in conventional SD organic solar cells (OSCs). Herein, an orthogonal solvent processed SD active layer with complete interpenetration was demonstrated by casting a nonfullerene acceptor Y6-HD solution on polymer donor Si25 film. The Si25/Y6-HD SD active layer could show unusually higher power conversion efficiency (PCE) in inverted OSCs compared to conventional devices. The Raman spectrum and time-of-flight secondary ion mass spectrometry analysis of the Si25/Y6-HD SD active layer revealed that the acceptor Y6-HD could penetrate into the donor Si25 layer to form a bulk-heterojunction (BHJ)-like morphology with complete interpenetration of donor and acceptor. Further investigations of more orthogonal solvent processed SD active layer materials helped to construct the complete interpenetration morphology and achieve high efficiency in the inverted SD OSCs. In particular, the D18-C16/Y6-BO SD active layer based on green solvents indane/tetrahydrofuran displayed a high efficiency of 16.23% in the inverted SD OSCs, which is not only the highest one for inverted SD OSCs but also one of the highest reported for SD OSCs processed with non-halogenated orthogonal solvents. This approach provides a new insight into the morphology of the SD active layer prepared using an orthogonal solvent and paves a way to achieve high performing inverted SD OSCs.