High‐Performance Ladder‐Type Heteroheptacene‐Based Nonfullerene Acceptors Enabled by Asymmetric Cores with Enhanced Noncovalent Intramolecular Interactions

Abstract

Nonfullerene acceptors (MQ3, MQ5, MQ6) are synthesized using asymmetric and symmetric ladder‐type heteroheptacene cores with selenophene heterocycles. Although MQ3 and MQ5 are constructed with the same number of selenophene heterocycles, the heteroheptacene core of MQ5 is end‐capped with selenophene rings while that of MQ3 is flanked with thiophene rings. With the enhanced noncovalent interaction of O⋅⋅⋅Se compared to that of O⋅⋅⋅S, MQ5 shows a bathochromically shifted absorption band and greatly improved carrier transport, leading to a higher power conversion efficiency (PCE) of 15.64 % compared to MQ3, which shows a PCE of 13.51 %. Based on the asymmetric heteroheptacene core, MQ6 shows an improved carrier transport induced by the reduced π–π stacking distance, related with the increased dipole moment in comparison with the nonfullerene acceptors based on symmetric cores. MQ6 exhibits a PCE of 16.39 % with a VOC of 0.88 V, a FF of 75.66 %, and a JSC of 24.62 mA cm−2.

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

“…As shown in Figure a, the dihedral angles between the central core and the terminal units of these NFAs varied between 7.9 and 16° with varying alkyl chain length, and both dihedral angels are the smallest for BTP-4F-C5-16 having the shortest alkyl chains, revealing the best planarity of BTP-4F-C5-16 that is conducive to intermolecular stacking. Note that these dihedral angle values obtained through MDS are bigger that those obtained by density functional theory (DFT) calculations, as the latter usually simplifies the long alkyl chains with short methyl or isobutyl groups to simplify the calculations, − where the influence of side chains has been underestimated. Without the simplification of alkyl chains during DFT calculations, the resulting dihedral angles are similar to the MDS results here. , …”

An acceptor with an asymmetric and extended conjugated backbone for high-efficiency organic solar cells with low nonradiative energy loss

“…In fact, in the past decade, the progress of OSCs was significantly driven by the invention of new active layer materials. 6,13,[41][42][43] Among them, molecules including donors and acceptors with the acceptor-donor-acceptor (A-D-A) architecture have demonstrated great success. 44 Presently, the rapid development of nonfullerene acceptors (NFAs) with A-D-A structures such as ITIC, Y6 and their analogues and derivatives has boosted the efficiencies of OSCs to a remarkable level.…”

M‐Series Nonfullerene Acceptors with Varied Fluorinated End Groups: Crystal Structure, Intermolecular Interaction, Charge Transport, and Photovoltaic Performance

“…[13][14][15][16] The dramatically improved photovoltaic performance of nonfullerenebased PSCs can be attributed to the merits of NFAs such as the tunable energy levels in a wider range, stronger absorption in the visible and near-infrared (NIR) region in comparison with the fullerene derivatives. [17][18][19] Since the first report of fused-ring electron acceptor (ITIC), [20] diverse structural variants, including side-chain adjustment, [21,22] core modification, [23][24][25] and end-group engineering, [24,26,27] have been widely employed to improve the performance of PSCs as well as to know the relationships between the molecular structure and the photovoltaic properties of NFAs. It has been proven that the end-group engineering not only can significantly impact the optical and electrochemical properties of the resulting acceptor molecule but also can play a vital role in determining the intermolecular π-πpacking arrangement as well as the resulting photovoltaic performance of PSCs.…”

“…Recently, our group reported a series of NFAs (M-series) based on ladder-type heteroheptacene without sp 3 -hybridized bridging atoms. [17,18,22,43] By controlling the bulkiness of neighboring side-chains on the fused-ring core, NFAs with appropriate aggregation behaviors were achieved, and they were subsequently used to fabricate PSCs with PCEs over 15%. So far, 1,1-dicyanomethylene-3-indanone (IC) with two fluorine atoms attached at the 5,6-positions is the most frequently used end group for the M-series acceptors.…”