Fullerene-free organic photovoltaics based on unconventional material combination: a molecular donor and polymeric acceptors

Abstract

In conventional organic photovoltaic cells, the active layer consists of a polymeric donor and a molecular acceptor (P_D/M_A). An unconventional material combination based on molecular donor/polymeric acceptor (M_D/P_A) emerged in 2014 but attracted limited attention. To broaden photovoltaic material systems and understand the crucial factors related to the photovoltaic performance, in this report, we adopted a molecular donor (p-DTS(FBTTh₂)₂) and three polymeric acceptors based on perylenediimide (PDI). We find that the high contents (70–80%) of p-DTS(FBTTh₂)₂ and the better crystallinity and larger grains in the blend films induced by the addition of 1,8-diiodooctane (DIO) play an important role in constructing the continuous and effective donor phase for charge transfer and hole transport in the active layers. The highest PCE of photovoltaic cells reached 3.01% with a V_OC of 0.68 V, J_SC of 7.59 mA cm⁻², and FF of 0.58 for the p-DTS(FBTTh₂)₂ : PSe-PDI active layer, although the hole and the electron mobilities are still unbalanced. Further optimization of the film morphology and improvement of the electron mobility by material design and device engineering are expected to boost the efficiency of M_D/P_A type fullerene-free solar cells.