Nanoscale Phase Separation in Ternary Organic Solar Cells Based on PTB7:PC70BM:IC70BA.

Abstract

As a fullerene derivative, IC₇₀BA is widely used in the ternary organic solar cells (TOSCs) to increase the open circuit voltage (V_oc) of the devices. Unfortunately, most of the literature shows that IC₇₀BA will lead to a reduction in the short-circuit current density (J_sc) and fill factor (FF). In this work, IC₇₀BA is added to the PTB7:PC₇₀BM binary system to form the ternary system, which is composed of one donor and two fullerene acceptors. Surprisingly, the addition of IC₇₀BA does not immediately lead to a decrease in J_sc and FF. In fact, the appropriate weight ratio of IC₇₀BA in fullerenes can simultaneously increase the V_oc, J_sc, and FF of the TOSCs. The synergistic optimization of the surface and bulk morphology of the ternary active layer suppresses the attenuation of J_sc and FF. The smooth surface and suitable phase separation size effectively guarantee the separation, transport and extraction of the charge. Moreover, the addition of IC₇₀BA can significantly improve the hole transport capacity of the active layer, and the optimal hole mobility is 5.13 - 10"4 cm²V^-1S^-1. Finally, the TOSCs with 10% weight ratio of IC₇₀BA gives the optimal PCE of 9.24% and ideality factor of 2.3.