Enhancing the performance of air-processed organic solar cells by formation of a ternary blend with an organic dye

Abstract

Organic solar cells (OSCs) have garnered attention for their processing simplicity, cost-effectiveness, and flexibility. This manuscript explores the incorporation of the organic dye Rhodamine B (RhB) into a binary blend of PTB7-Th:PC₇₀BM, forming air-processed ternary blend OSCs with an inverted architecture. The choice of PTB7-Th:PC₇₀BM is driven by its record efficiency exceeding 10 % and compatibility with RhB in terms of photon absorption range and energy level alignment. With an optimal RhB weight content of 0.2 %, the ternary OSCs exhibit a 27 % enhancement in power conversion efficiency (PCE) compared to binary devices. This enhancement is mainly caused by a 13 % increase in short-circuit current density (J_SC) and an 11 % increase in fill factor (FF). Steady-state photoluminescence, transient absorption and incident photon-to-current conversion efficiency (IPCE) measurements revealed the role of Förster Resonance Energy Transfer (FRET) from RhB to PTB7-Th in contributing to the higher photocurrent in the ternary devices. The improved FF and the enhancement in IPCE at wavelengths where RhB does not absorb suggest enhanced charge generation and transport due to more optimal blend morphology from better chain ordering, as inferred from grazing incidence X-ray diffraction (GIXRD). Furthermore, the ternary blend displays enhanced photochemical stability and improved device stability under 1 sun illumination in the presence of oxygen. These findings underscore the potential of incorporating organic dyes in OSCs to achieve improved performance and enhanced stability, addressing a critical challenge to the commercial viability of these promising photovoltaic devices.