High-Performance Poly(3-hexyl thiophene)-Based Organic Photovoltaics with Side-Chain Engineering of Core Units of Small Molecule Acceptors

Bin Chang; Chung-Hao Chen; Ting-Fang Hsueh; Shaun Tan; Yu-Che Lin; Yepin Zhao; Bing-Shiun Tsai; Ting-Yi Chu; Yu-Ning Chang; Ching-En Tsai; Cheng-Sheng Chen; Kung-Hwa Wei

doi:10.1021/acsami.3c13007

High-Performance Poly(3-hexyl thiophene)-Based Organic Photovoltaics with Side-Chain Engineering of Core Units of Small Molecule Acceptors

ACS Appl Mater Interfaces. 2023 Nov 3. doi: 10.1021/acsami.3c13007. Online ahead of print.

Authors

Affiliations

¹ Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan.
² Department of Materials Science and Engineering, University of California─Los Angeles, Los Angeles, California 90095, United States.

PMID: 37923367
DOI: 10.1021/acsami.3c13007

Abstract

In this study, we synthesized a series of four large-band gap small molecule acceptors with side-chain engineering of the dithieno-pyrrolo-fused pentacyclic benzotriazole (BZTTP or Y1 core) or the fused-ring dithienothiophene-pyrrolobenzothiadiazole (TPBT or Y6 core) with difluoro-indene-dione (IO2F) or dichloro-indene-dione (IO2Cl) end groups to form Y1-IO2F, Y1-IO2Cl, Y6-IO2F, and Y6-IO2Cl acceptors, respectively, for blending with poly(3-hexyl thiophene) (P3HT) for bulk heterojunction organic photovoltaics. The complementary UV-vis absorption spectra of these small molecules and P3HT along with their offset energy bands allow broad absorption and effective electron transfer. Through synchrotron wide-angle X-ray scattering (WAXS) analyses and contact angle measurements, we found that the blend of the small molecule Y6-IO2F (having a TPBT core) and P3HT achieves an optimum morphology that balances their crystallinity and miscibility, among those of these four blends, leading to a substantial enhancement in the short-circuit current density and thus power conversion efficiency (PCE) in their devices. For example, the P3HT:Y6-IO2F (w/w: 1/1.2) device exhibited a champion PCE of 10.5% with a short current density (J_sc) value of 15.9 mA/cm² as compared to the P3HT:Y1-IO2F device having a PCE of 2.2% with a J_sc value of 5.7 mA/cm² because of the higher Y6-IO2F (with TPBT core) molecular packing that facilitated carrier transport in the devices. The enhanced thermal stability exhibited by the devices incorporating Y6-IO2F and Y6-IO2Cl, as compared to that of Y1-IO2F and Y1-IO2Cl devices, is also due to the more planar TPBT core structure, while the photostability of devices incorporating Y6-IO2Cl and Y1-IO2Cl is better than that of devices incorporating Y6-IO2F and Y1-IO2F, owing to more photostable chemical structures. These results present an outstanding performance for P3HT-based organic solar cells. Moreover, these small molecule blends are processed with an environmentally friendly solvent tetrahydrofuran, demonstrating both the sustainability and commercial viability of these types of organic photovoltaics.

Keywords: high short-circuit current density; miscibility; side chain engineering; small molecule acceptor core; thermal stability.