Effects of Short‐Axis Alkoxy Substituents on Molecular Self‐Assembly and Photovoltaic Performance of Indacenodithiophene‐Based Acceptors

Abstract

Side chain design is an important part of the acceptor-donor-acceptor (A-D-A)-structured small molecule acceptors (SMAs), it often affects not only self-assembly of SMAs but also the mesoscale morphology of active layer of polymer solar cells (PSCs). Here, we systematically investigated the influence of the side chain length on the physicochemical properties, single-crystal packing of the SMAs, active layer morphology and photovoltaic performance of PSCs based on a series of SMAs (IDIC-2F, MO-IDIC-2F, HO-IDIC-2F and DO-IDIC-2F). It is found that the intermolecular aggregation property of these SMAs are strongly correlated with side chain lengths. With the increase of alkoxy chain length from IDIC-2F to DO-IDIC-2F, the ordered aggregation of these SMAs in films is enhanced gradually, according to the UV-vis absorption spectra and GIWAXS measurement. The single-crystal diffraction of these SMAs further reveals that small changes in side chains can have a dramatic impact on molecular self-assembly and assist in understanding of the charge transport properties of these SMAs. The power conversion efficiency (PCE) values of the corresponding PSCs show a linear increase with the increase of side chains length, and the simultaneously and gradually increased J sc values were the dominant factors responsible for this correlation. The π-π coherence length of the SMAs in the active layers is increased, which could be the reason for the increase of the J sc in the PSCs. Our results indicate that This article is protected by copyright. All rights reserved. 3 small changes in side chain length can have a dramatic impact on the molecular self-assembly, morphology and performance of the PSCs. The structure-performance relationship established in this study can provide important instructions for the side chain engineering and for the design of efficient SMAs materials.

Introducing a Phenyl End Group in the Inner Side Chains of A‐DA'D‐A Acceptors Enables High‐Efficiency Organic Solar Cells Processed with Nonhalogenated Solvent

“…This can be demonstrated by the changes in the shoulder peaks exhibited by L8‐BO and L8‐Ph at ≈710–750 nm. From L8‐BO to L8‐Ph, the decreased intensity of the shoulders elucidates a gradually increased J ‐type aggregation of molecules, [ 29–31 ] which is mainly owing to that the phenyl‐alkyl side chains may provide more abundant intermolecular interaction to modulate the molecules to form more ordered packing. And more ordered molecular packing will be beneficial to efficient charge transport.…”

Influence of Large Steric Hinderance Substituent Position on Conformation and Charge Transfer Process for Non‐Fused Ring Acceptors

“…The selected molecules in single crystal and their relative positions are depicted in Figure 4c,f. The electron ( t e ) and hole ( t h ) transfer integrals were calculated through energy splitting method, [ 11,26 ] and the calculations were carried out under CAM‐B3LYP/6‐31G (d, p) level to accurately estimate the exchange correlation interaction. As shown in Table 3 , the t e and t h values for three adjacent A4T‐25 molecules are 66.94/35.37 (1–2) and 0.68/2.04 (1–3) meV, indicating effective charge transfer may occur in the laminate‐like secondary structure and becomes much weaker toward outside.…”

“…Single-crystal data offers a deep insight into the relationship between molecular geometries and intermolecular packing modes, which can help to further understand the electron transfer process. Although single-crystal data of many fused ring acceptors are collected, [11,12,15,24] few were reported for non-fused ring acceptors. [25] Herein, we obtained the single crystal of A4T-25 and A4T-26 by using vapor diffusion method.…”

The effects of the side-chain length of non-fullerene acceptors on their performance in all-small-molecule organic solar cells

“…2(f), other obvious out-of-plane peaks at 0.95 Å −1 (200, d ∼ 6.61 Å) and 0.76 Å −1 (300, d ∼ 8.27 Å) appear in FC10-2Cl neat films, and 1.49 Å −1 (200, d ∼ 4.22 Å), 1.00 Å −1 (300, d ∼ 6.28 Å) and 0.93 Å −1 (400, d ∼ 6.76 Å) appear in FC12-2Cl neat films, suggesting the presence of longer-distance π–π stacking in their pristine films and more molecules stack regularly in the out-of-plane direction. 53,54 Furthermore, estimated from the Scherrer equation, 55 crystal coherence length (CCL) values of (010) diffraction are 14.24, 24.59, 30.73, 30.90 and 35.34 Å for FC4-2Cl, FC6-2Cl, FC8-2Cl, FC10-2Cl and FC12-2Cl, respectively, indicating that these NFAs with longer side chains can form relatively larger (010) ordered stacking in their pristine films. 56 The discussion above is closely linked to the FF of the corresponding OSCs.…”