Issue 18, 2020

Enhanced efficiency and stability of nonfullerene ternary polymer solar cells based on a spontaneously assembled active layer: the role of a high mobility small molecular electron acceptor

Abstract

It is challenging to afford efficient and stable organic solar cells based on an as-cast active layer without any external treatments. We present a planar organic electron acceptor, BPTCN, with high electron mobility as a third component in nonfullerene ternary polymer solar cells, which comprises an electron-deficient 4,7-bis(5H-4,6-dioxothieno[3,4-c]pyrrol-1-yl)benzo[c][1,2,5]thiadiazole core, doubly endcapped by 2-(3-ethyl-5-methylene-4-oxothiazolidin-2-ylidene)malononitrile through the alkylated thiophene-2,5-ylene unit. It shows a π–π stacking distance of 3.60 Å and μe of 1.31 × 10−3 cm2 V−1 s−1. BPTCN exhibits an absorption maximum at 569 nm in the as-cast film and good miscibility with the NIR-absorption acceptor COi8DFIC, leading to complete förster energy transfer in the blends. Adding BPTCN into the PTB7-Th:COi8DFIC blend produces multiple beneficial effects: (i) facilitating exciton dissociation and charge transfer at the donor/acceptor interface while suppressing bimolecular and trap-assisted recombination, as revealed by analysis of the JphVeff, JscIlight and VocIlight characteristics, (ii) increasing hole and in particular electron transport; and (iii) generally promoting the crystallinity of the polymer donor PTB7-Th, as revealed by grazing incidence X-ray diffraction results. Moreover, the phase purity is greatly improved in the ternary blend PTB7-Th : COi8DFIC : BPTCN (1 : 1.05 : 0.45 by weight). Consequently, the tentatively optimized ternary solar cell provides a PCE of 11.62% with a Voc = 0.74 V, Jsc = 25.93 mA cm−2 and FF = 60.61% in comparison with the binary systems PTB7-Th:COi8DFIC (PCE of 9.41%) and PTB7-Th:BPTCN (6.42%) in the absence of any extra treatments. After thermal aging at 80 °C for 450 h, this ternary solar cell exhibits increased stability with the PCE retaining 84.39% of the initial value.

Graphical abstract: Enhanced efficiency and stability of nonfullerene ternary polymer solar cells based on a spontaneously assembled active layer: the role of a high mobility small molecular electron acceptor

Supplementary files

Article information

Article type
Paper
Submitted
14 yan 2020
Accepted
23 mar 2020
First published
24 mar 2020

J. Mater. Chem. C, 2020,8, 6196-6202

Enhanced efficiency and stability of nonfullerene ternary polymer solar cells based on a spontaneously assembled active layer: the role of a high mobility small molecular electron acceptor

D. Luo, M. Zhang, J. Li, Z. Xiao, F. Liu, L. Ding and X. Zhu, J. Mater. Chem. C, 2020, 8, 6196 DOI: 10.1039/D0TC00225A

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