Enhanced Self-Stimulated Dissociation in Non-fullerene Layer-by-Layer Organic Solar Cells through Superimposed and Oriented Dipolar Polarization

Abstract

A non-fullerene layer-by-layer (LBL) structure can establish effective donor/acceptor (D/A) interfaces and lead to remarkable photovoltaic efficiencies based on facile solution processing properties, as compared with nonfullerene bulk heterojunction devices. However, the operating mechanisms have been remaining as an unaddressed issue to understand the role of D/A interfaces toward developing photovoltaic processes in non-fullerene LBL where the high electrically polarizable non-fullerene molecules exist. Here, we address the operating mechanisms of photovoltaic actions by in situ monitoring the dynamic D/A interfaces upon selectively exciting the non-fullerene acceptor layer to address the effects of optically induced superimposed and oriented dipoles on electron−hole pair self-stimulated dissociation in non-fullerene LBL organic solar cells [ITO/PEDOT:PSS/PM6/Y6/PDIN/Al]. Essentially, the self-stimulated dissociation at the D/A interfaces can be monitored by magneto-photocurrent while separately exciting the donor and acceptor components with two different laser beams. We observed an interesting phenomenon that optically exciting the non-fullerene Y6 acceptor component leads to easier electron−hole dissociation at D/A interfaces and consequently an increase on electron−hole pair self-stimulated dissociation to generate photocurrent in non-fullerene LBL solar cells. This phenomenon presents a hypothesis that optically exciting the compactly stacked non-fullerene Y6 molecules induces superimposed and oriented electrical dipoles within A−D−A−D−A structures to increase the self-stimulated dissociation at D/A interfaces toward developing the photovoltaic actions in non-fullerene LBL solar cells. This hypothesis is supported by our photoinduced capacitance result: photoexcitation increases bulk polarization in the dipolar polarization zone in non-fullerene LBL solar cells. Furthermore, optically generated dipoles are verified by photoinduced magnetocapacitance, solely generated by photoinduced polarization rather than photogenerated carriers, in non-fullerene LBL PM6/Y6. Clearly, the optically generating superimposed and oriented electrical dipoles become a critical parameter to operate the photovoltaic actions at D/A interfaces in non-fullerene LBL solar cells.