Benzobis(Thiazole)-Based Conjugated Polymer with Varying Alkylthio Side-Chain Positions for Efficient Fullerene-Free Organic Solar Cells

Abstract

Alkylthio groups can be used to modulate energy levels and molecular packing of organic semiconductors, which makes it important in the design of materials for organic solar cell. However, its effect has not been sufficiently exploited as most of the studies report introducing an alkylthio group to the donor unit and seldom to the acceptor unit of donor−acceptor conjugated polymers. In this report, two alkylthio-substituted polymers, namely, PBB-TSA and PBB-TSD, with benzo[1,2-d:4,5-d′]bis(thiazole) (BBT) as the acceptor unit and benzo[1,2-b:4,5-b′]dithiophene (BDT) as the donor unit, were rationally designed, synthesized, and applied in organic photovoltaics. An alkylthio side chain was substituted on the BBT-accepting unit for PBB-TSA, while for PBB-TSD, the alkylthio side chain was substituted on the BDT donor unit. PBB-TSA and PBB-TSD show upshifted and downshifted energy levels, respectively, compared to the nonsulfursubstituted material. Both polymers exhibit dominate face-on orientation, while PBB-TSD exhibits higher crystallinity compared to PBB-TSA. With the contribution of lower energy level and beneficial film morphology, the device based on PBB-TSD/IT-4F has much higher power conversion efficiency (PCE) of 14.6%, whereas the PBB-TSA blend had a lower PCE of 10.7%. 1,8-Diiodooctane can effectively optimize the blend film morphology, and the effect on device performance has also been demonstrated in detail. This result indicates that introducing an alkylthio side chain into the donor or acceptor moieties would result in materials with different energy levels and thus would be utilized to match with various acceptors, achieving optimized performance in organic solar cells.

Recent Advances in Organic Photovoltaic Materials Based on Thiazole‐Containing Heterocycles

“…In 2021, Bao et al synthesized two alkylthio‐substituted polymers, PBB‐TSA and PBB‐TSD, whose alkylthio side chains were, respectively, substituted on the BBTz unit and BDT unit to modulate energy levels and molecular packing. [ 102 ] Compared to PBB‐H, PBB‐TSA and PBB‐TSD showed upshifted and downshifted energy levels, respectively. Both polymers exhibited dominant face‐on orientation, while PBB‐TSD exhibited higher crystallinity compared to PBB‐TSA.…”

18.6% Efficiency All‐Polymer Solar Cells Enabled by a Wide Bandgap Polymer Donor Based on Benzo[1,2‐d:4,5‐d′]bisthiazole

“…[37] Polymers based on the former are well-studied, [37] while those with the latter have been poorly developed. [38][39][40][41][42][43][44] Chen et al have demonstrated 4,8-BBTz based polymers could obtain high mobilities, long exciton lifetimes, pure domains, and dominant face-on orientation when blending with Y6, thus delivering decent PCEs over 15%. [40] The results demonstrated the application poten-tial of BBTz-based polymers in SMA-based OSCs.…”

Manipulation and Direct Characterization of Polymer/Small-Molecule Interface Morphology in Bulk-Heterojunction Solar Cell

“…The device performance of organic photovoltaics (OPVs) has improved remarkably owing to the recent development of novel light-harvesting materials. − Nonfullerene structured acceptors (NFAs) such as ITIC and Y6, employed as n -type materials in OPVs, provide complementary absorption with p -type conjugated polymers (CPs) and enable one to maximize light-harvesting capabilities and enhance the power conversion efficiency (PCE). − The efficacy of NFAs is more pronounced in OPVs with a bulk-heterojunction (BHJ) architecture where NFA ( n -types) and CP ( p -types) are intermixed at a nanoscale. , Therefore, the development and application of new NFAs are of interest to further improve the OPV performance. Because NFAs are adopted as electron acceptors in BHJ OPVs, their working mechanism is the same as that of fullerene derivatives. , This indicates that managing the film morphology composed of CPs and NFAs, such as the interfacial area, domain size, and crystallinity of individual domains, has a decisive effect on the OPV performance. , Therefore, understanding the interface properties between CPs and NFAs is essential for devising efficient light-harvesting materials for BHJ-type OPVs.…”