Substitution Effect on Thiobarbituric Acid End Groups for High Open-Circuit Voltage Non-Fullerene Organic Solar Cells

Abstract

Recent advances in non-fullerene acceptors (NFA) have resulted in significant improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In our efforts to boost opencircuit voltage (V OC ) for OSCs, the molecular design employing thiobarbituric acid (TBTA) end groups and a IDTT core gives rise to 1 NFA with significantly raised lowest unoccupied molecular orbital (LUMO) energy level, which, when paired with PCE10, can achieve V OC s over 1.0 V and decent PCEs that outperform the equivalent devices based on the benchmark ITIC acceptor. While the use of TBTA end group is effective in tuning energy levels, very little is known about how the alkyl substitution on the TBTA group impacts the solar cell performance. To this end, TBTA end groups are alkylated with linear, branched, and aromatic sidechains in an effort to understand the influence on thin film morphology and related device performances. Our study has confirmed the dependence of solar cell performance on the end group substituents. More importantly, we reveal the presence of an ideal window of crystallinity associated with the medium length hydrocarbon chains such as ethyl and benzyl. Deviation to the shorter methyl group makes the acceptor too crystalline to mix with polymer donor and form proper domains, whereas longer and branched alkyl chains are too sterically bulky and hinder charge transport due to nonideal packing. Such findings underline the comprehensive nature of thin film morphology and the subtle end group effects for the design of non-fullerene acceptors.

Tuning optical properties of triphenylamine‐pyrrole by alkyl‐substituted thiobarbituric acid for dye‐sensitized solar cell

“…In order to check the amount of the intramolecular charge transfer in TBT derivatives, the atomic charges were computed using Hirshfeld and Mulliken method (Table 4). The calculated charge values show that the N ‐ethyl and N ‐benzyl derivatives accept more electrons than other acceptors, which could be injected later to the TiO 2 CB, which is in agreement with the experimental results for IDTT system 35 …”

Boosting photovoltaic performance of ternary organic solar cells by integrating a multi-functional guest acceptor

“…3a, strong out-of-plane (OOP) π-π diffraction peaks are observed at 1.717 Å -1 and 1.704 Å -1 for Y6 and PM6 neat films, respectively, indicating good crystallinity and preferred face-on orientation, consistent with the reported results [16,61,62]. In comparison with Y6, the pristine Y-T film shows a preferential edge-on orientation and a weak in-plane (IP) π-π diffraction peak was found at 1.609 Å -1 with a d-spacing of 3.905 Å, suggesting that the crystallinity and molecular orientation of acceptors can be tuned by end group engineering [63]. The corresponding line-cut intensity profiles along the OOP and IP directions are described in Fig.…”

Pyrrole/thiophene π‐bridged two triphenylamine electron donor and substituted thiobarbituric electron acceptor for D‐π‐A‐D‐featured DSSC applications

“…The electron acceptor moiety was dialkyl‐substituted thiobarbituric acid to explore the electron mobility and the anchoring capability on the semiconductor (TiO 2 ) surface. [ 20 ] For comparison, we choose the widely used cyanoacrylic‐anchoring group. The geometry of the dyes were explored with the B3LYP/6‐311g(d) level of theory and followed by the frequency calculations.…”