Air-processed high performance ternary blend solar cell based on PTB7-Th:PCDTBT:PC70BM

•Optical, electrical and morphological properties of ternary system were investigated.•The hole mobility was improved by incorporating a 20% content of PCDTBT to PTB7-Th.•The PCE and stability of ternary organic solar cells was enhanced compared with the binary devices.

Ternary bulk heterojunctions (BHJs) are promising candidates that can improve the power conversion efficiencies (PCEs) of organic solar cells (OSCs). In this paper, a ternary OSC with two donors, including one wide bandgap polymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), one low bandgap polymer Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th), and one acceptor [6,6]-phenyl C70 butyric acid methyl ester (PC70BM), is fabricated in atmospheric conditions. By incorporating a 20% content of PCDTBT, an optimized PCE of 7.86% for ternary OSC is characterized by a short-circuit current density (Jsc) of 15.21 mA cm−2, a fill factor of 69.70% and an open-circuit voltage (Voc) of 0.74 V. The Voc values increased steadily from 0.73 to 0.86 V as the increase of PCDTBT fraction, which indicates that the Voc of ternary OSC is not limited by the smallest one of the corresponding binary OSC. We show that the Jsc of the ternary OSC is better than those of the binary OSC in virtue of the complementary polymer absorption and cascade energy levels, as well as optimized morphology of the ternary system. Furthermore, the lifetime of the devices with PCDTBT is greatly enhanced. This work indicates that two donors (PTB7-Th/PCDTBT) ternary BHJs system provide a simple and effective method to improve the performance and also the stability of OSCs.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide