Alkyl Chain Tuning of Non-fullerene Electron Acceptors toward 18.2% Efficiency Binary Organic Solar Cells

Abstract

Tailoring of the chemical structure is an effective method to tune the aggregation and optoelectronic properties of organic photovoltaic materials to boost the performance of organic solar cells (OSCs). Here, four non-fullerene electron acceptor materials, namely, BTP-4F-C8-16, BTP-4F-C7-16, BTP-4F-C6-16, and BTP-4F-C5-16, with different lengths of alkyl chain on the bithiophene units were synthesized, and the impact of chain length on the intermolecular stacking, nanoscale phase separation with polymer donors, optoelectronic properties, and device performance were investigated. Molecular dynamics simulations and experimental exploration show that reducing the chain length from n-octyl (C8) to n-pentyl (C5) can enhance the molecular planarity, shorten the π−π stacking distance, and improve the electron mobility, consequently leading to enhanced structural order, charge mobility, and appropriate phase separation in the blend with PM6, contributing to the achievement of the best power conversion efficiency of 18.20% with a V OC of 0.844 V, a fill factor of 77.68%, and a J SC of 27.78 mA cm −2 , which is one of the highest efficiencies of single-junction binary OSCs reported in the literature so far.

Strong Intermolecular Interactions Induced by High Quadrupole Moments Enable Excellent Photostability of Non‐Fullerene Acceptors for Organic Photovoltaics

“…Organic photovoltaics (OPVs) have seen impressive efficiency improvements in the last few years due to the development of non‐fullerene acceptors (NFAs), particularly the new Y6 (2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐ e ]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐ g ]thieno[2′,3′:4,5]thieno[3,2‐ b ]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1 H ‐indene‐2,1‐diylidene))dimalononitrile) family, which has achieved efficiencies of over 18%. [ 1,2 ] However, the poor operational lifetimes of many high performing NFAs limit their use in commercial modules. It is therefore important to understand the degradation mechanisms of these acceptors to enable the synthesis of more stable acceptor materials.…”

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indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1Hindene-2,1-diylidene))dimalononitrile) family, which has achieved efficiencies of over 18%. [1,2] However, the poor operational lifetimes of many high performing NFAs limit their use in commercial modules. It is therefore important to understand the degradation mechanisms of these acceptors to enable the synthesis of more stable acceptor materials.One of the most popular acceptor families is based on ITIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno [1,2-b:5,6-b′]dithiophene), which utilizes a fused conjugated IDTT (indacenodithienothiophene) core with strongly electron-withdrawing INCN (2-(3oxo-2, 3-dihydroinden-1-ylidene) malononitrile groups on the periphery, and out of plane 4-hexylphenyl sidechains that are used to limit π-π stacking and reduce self-aggregation in the blend.

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“…indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1Hindene-2,1-diylidene))dimalononitrile) family, which has achieved efficiencies of over 18%. [1,2] However, the poor operational lifetimes of many high performing NFAs limit their use in commercial modules. It is therefore important to understand the degradation mechanisms of these acceptors to enable the synthesis of more stable acceptor materials.…”

Novel Pyrrolo [3,4‐b] Dithieno [3, 2‐f:2″,3″‐h] Quinoxaline‐8,10 (9H)‐Dione Based Wide Bandgap Conjugated Copolymers for Bulk Heterojunction Polymer Solar Cells

“…[1][2][3][4][5][6] After the progress of non-fullerene small molecule acceptors (NFSMAs), [7][8][9][10] especially Y6 series, [11,12] the power conversion efficiency (PCE) has been managed in the range of 18-19%. [13][14][15][16][17] It is projected that the PCE can be boosted up to 20% when BHJ active layer consists of the appropriate donor and acceptor. [18,19] It has prospective commercialization for the forthcoming photovoltaic technology.…”

Selection of side groups on simple non‐fullerene acceptors for the application in organic solar cells: From flexible to rigid

“…In 2019, the new‐generation FREAs, that is, Y‐series acceptors, which adopt the backbone of A‐D 1 A′D 1 ‐A, were reported 15–17 . Due to the quinoid effect of their electron‐deficient A′ cores, for example, benzothiadiazole and benzotriazole, Y‐series acceptors would show narrower bandgaps and lower energy losses than the first‐generation FREAs, giving PCEs over 18% for the resultant OSCs 18–22 . A lot of researches have disclosed that, in addition to the conjugated backbones, side groups on Y‐series acceptors also influence greatly their photovoltaic properties by regulating molecular packing and molecular orientation 19,23–27 .…”