The exquisite design and persistent development of fused-ring-acceptor-unit-based copolymer donors and Y-series nonfullerene acceptors (NFAs) have pushed the power conversion efficiencies (PCEs) for organic solar cells onto the 18% level[1-21]. Our group invented copolymer donors D18 and D18-Cl[2, 3]. D18:Y6, D18-Cl:N3 and D18:N3 solar cells have delivered outstanding PCEs of 18.22%, 18.13% and 18.56%, respectively[2-4]. Ternary solar cells based on a polymer donor, a NFA and a fullerene acceptor show great potential since they combine good light-harvesting capability of NFA and good electron-mobility of fullerene[5].
In this report, the device structure is ITO/PEDOT:PSS/D18-Cl:N3:PC61BM (D:A1:A2)/PDIN/Ag. The D : A1 ratio was fixed at 1 : 1.4 (wt) since D18-Cl:N3 cells gave the best performance at the ratio of 1 : 1.4[3]. We adjusted PC61BM content from 0.1 to 0.2 to 0.3. When D : A1 : A2 ratio was 1 : 1.4 : 0.1, the ternary cells gave the highest PCE (Table S1). The champion cells with 0.3 vol% diphenyl ether (DPE) as the additive and an active layer thickness of 114 nm gave the highest PCE of 18.69%, with an open-circuit voltage (Voc) of 0.849 V, a short-circuit current density (Jsc) of 28.22 mA cm–2 and a fill factor (FF) of 78.0% (Table S2, Table S3 and Fig. S1). The external quantum efficiency (EQE) exceeded 80% in 450–840 nm, with a maximum of 91% at 540 nm (Fig. S2). The integrated photocurrent density is 27.24 mA cm–2. The best devices were also measured at the National Institute of Metrology (NIM), Beijing, and a certified PCE of 18.1% (Voc, 0.854 V; Jsc, 27.36 mA cm–2; FF, 77.3%; effective area, 2.580 mm2) was recorded (Fig. S3). To the best of our knowledge, the 18.1% certified efficiency is the highest value reported for organic solar cells to date. Compared with the binary cells, the ternary cells show simultaneously enhanced Jsc and FF, suggesting the improved charge transport in the active layer. We measured hole and electron mobilities (μh and μe) by using the space charge limited current (SCLC) method (Fig. S4, Fig. S5 and Table S4). From binary to ternary blend films, μh didn’t change much while μe increased from 6.32 × 10–4 to 7.42 × 10–4 cm2 V–1 s–1. Fullerene enhanced electron transport and led to more balanced charge transport (Table S4).
Acknowledgements
We appreciate the National Key Research and Development Program of China (2017YFA0206600) and the National Natural Science Foundation of China (51773045, 21772030, 51922032, 21961160720) for financial support.
Appendix A. Supplementary material
Supplementary materials to this article can be found online at
