Regulation of Molecular Orientations of A–D–A Nonfullerene Acceptors for Organic Photovoltaics: The Role of End‐Group π–π Stacking

Abstract

Increasing horizontal and face-on orientations of the active molecules in organic solar cells is critical to improve light absorption, charge mobility, and exciton diffusivity for high photovoltaic efficiency. However, how to effectively control the molecular orientations is challenging and still unclear.Here, the molecular self-assembly and orientation formation are elucidated for a series of acceptor-donor-acceptor (A-D-A) small-molecule acceptors (SMAs) by atomistic molecular dynamics simulations. The results indicate that the A-D-A molecules tend to assemble via the end-group π-π stacking at the liquid-vapor interfaces during solvent evaporation, which is beneficial to enhance horizontal and face-on orientations. Remarkably, the order of both horizontal and face-on orientations in the films shows a good linear correlation with the number of π-π stacking among all the A-D-A SMAs. The π-π stacking is found to be cooperatively controlled by both the end-group π-π interaction and side-chain steric hindrance. This work provides the rationalization for the different molecular orientations in a wide range of A-D-A SMAs and is useful to improve the horizontal and face-on orientations for high-performance organic photovoltaics.

Enabling Donor: Acceptor Bicontinuous Networks via Short Contacts in Double‐Cable Polymers with Pendant Rylene Diimides

“…[45][46][47] Accordingly, the atomic charges were fit with the restrained electrostatic potential (RESP) method obtained by denisty functional theory (DFT) calculations at the B3LYP/cc-PVTZ level. [48][49][50][51] The torsion potential of DCPs was reparametrized according to DFT calculations (Figure S15, Supporting Information), and the fitting method was used as described in our previous work. [52] The simulations were carried out with 3D periodic boundary conditions; the leap-frog integrator with a time step of 1.0 fs was selected.…”

Truxene π-Expanded BODIPY Star-Shaped Molecules as Acceptors for Non-Fullerene Solar Cells with over 13% Efficiency

“…Over the past few decades, fullerenes and their derivatives, such as [6,6]-phenyl-C 61 /C 71 -butyric acid methyl ester (PC 61 BM/PC 71 BM), have been employed as electron acceptors in OSCs, owing to their strong electron-accepting ability, high electron mobility, and isotropy of charge transport derived from their three-dimensional cage structure. − However, the attention in the progress of OSCs has changed to non-fullerene small-molecule acceptors (NFSMAs) in recent years owing to the inherent limitations of fullerene acceptors involving inadequate energy level modification, poor photostability, poor absorption in the visible and NIR regions, and morphology instability. Compared with the fullerene acceptors, NFSMAs exhibit many distinct advantages, such as low-cost production, quickly adjustable energy levels suitable for various high-performance donor materials, a strong absorption profile covering both visible and NIR regions of the solar spectra, good chemical stability and photostability, high morphological stability, and better adjustment with donors to form a suitable morphology. − …”

“…As a consequence of these strategic properties, many efforts have been dedicated to developing novel NFSMAs and employing them in OSCs. ,, Among numerous NFSMAs, the fused-ring electron acceptors (FREAs) have been demonstrated as the most efficient for realizing high power conversion efficiency (PCE). ,,,, In particular, the invention of the breakthrough molecule ITIC with an A–D–A design in 2015 introduces a new era of this research field of OSCs . The fused-ring electron acceptors recently underwent rapid development, and PCE in NFSMA-based OSCs now has exceeded 18%. − Nevertheless, FREAs usually require multiple synthesis phases leading to poor overall yields and high costs, which is disadvantageous to large-scale commercial applications in the forthcoming OSC devices. ,− Therefore, exploring new NFSMAs with easy synthesis toward high-performance organic solar cells will be essential and desirable.…”

“…12,18,19 Among numerous NFSMAs, the fused-ring electron acceptors (FREAs) have been demonstrated as the most efficient for realizing high power conversion efficiency (PCE). 8,12,17,20,21 In particular, the invention of the breakthrough molecule ITIC with an A− D−A design in 2015 introduces a new era of this research field of OSCs. 22 The fused-ring electron acceptors recently underwent rapid development, and PCE in NFSMA-based OSCs now has exceeded 18%.…”

Enhanced Performance of Cyclopentadithiophene-Based Donor-Acceptor-Type Semiconducting Copolymer Transistors Obtained by a Wire Bar-Coating Method

“…In recent decades, solution-processable polymer field-effect transistors (PFETs) based on conjugated copolymers with donor-acceptor (D-A)-type moieties, such as indacenodithiophene (IDT) [ 1 , 2 ], diketopyrrolopyrrole (DPP) [ 3 , 4 ], isoindigo (IDG) [ 5 , 6 ], naphthalenediimide (NDI) [ 7 , 8 , 9 ], and cyclopentadithiophene (CDT) [ 10 , 11 , 12 ], have received extensive attention due to their remarkably high field-effect mobilities exceeding 10 cm 2 V −1 s −1 and low-energy bandgap characteristics. Rigid and nearly torsion-free planar polymer backbones in the D-A-conjugated copolymers have been regarded to be attributed to the enhanced charge transport along the chain and efficient interchain charge transfer through the strong π-π interaction between adjacent D-A subunits [ 13 , 14 , 15 ]. Several approaches, such as designing the D-A building blocks for controlling the push-pull strength of donor and acceptor moieties [ 16 , 17 ] and modification of the side chains [ 18 ], have been suggested for improving the molecular-structure of D-A-conjugated copolymers and electrical properties.…”