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. Issue 18 (9th April 2020)

• Record Type: Journal Article
• Authors: Luo, Dou; Zhang, Ming; Li, Jian-Bin; Xiao, Zuo; Liu, Feng; Ding, Liming; Zhu, Xu-Hui
• Is Part Of: Journal of materials chemistry. Volume 8:Issue 18(2020)
• Page Start: 6196
• Page End: 6202
• Publication Date: 2020-04-09
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d0tc00225a
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Introducing a medium bandgap electron acceptor into the PTB7-Th:CO i 8DFIC solar cell increases both thermal stability and PCE without external treatments. 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(5 H -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 μ e of 1.31 × 10 −3 cm 2 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 CO i 8DFIC, leading to complete förster energy transfer in the blends. Adding BPTCN into the PTB7-Th:CO i 8DFIC 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 J ph – V eff, J sc – I light and V oc – I light 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 : CO i 8DFIC : BPTCN (1 : 1.05 : 0.45 by weight). Consequently, the tentatively optimized ternary solar cell provides a PCE of 11.62% with a V oc = 0.74 V, J sc = 25.93 mA cm −2 and FF = 60.61% in comparison with the binary systems PTB7-Th:CO i 8DFIC (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.