Miscibility driven morphology modulation in ternary solar cells

Abstract

Organic solar cells (OSCs) are viable power sources for photovoltaic applications. In this work, a non-fullerene acceptor, PDI-EH, was designed to form a nearly orthogonal structure to suppress its aggregation, and integrated into ternary OSCs. In addition to enhanced photon absorption and matched charge cascade, a PDI-EH acceptor modulated the morphology, which is crucial to affect device efficiency. Detailed analysis revealed that PDI-EH can fine-tune the miscibility of the host donor and acceptor (D/A) materials to form an optimally intermixed phase with short-range molecular order. Photo-induced force microscopy (PiFM) for selective PiFM imaging of D/A materials provided strong evidence that D/A materials formed well-mixed films after PDI-EH incorporation. Additionally, nanoscale spatial mapping of charge carrier dynamics was realized for the first time in a ternary film using a novel transient photo-response atomic force microscopy (TP-AFM) technique. The resulting TP-AFM data revealed a reduced charge transport time, increased charge recombination lifetime and extended charge diffusion length. These improvements brought about by PDI-EH benefit the photovoltaic performance of ternary OSCs under both 1-sun and indoor illuminations. Our work offers insights into morphology modulation and the resulting local charge carrier dynamic, thereby facilitating the development of OSCs in practical applications.