Synergetic Effect of Side-Chain Engineering of Polymer Donors and Conformation Tuning of Small-Molecule Acceptors on Molecular Properties, Morphology, and Photovoltaic Performance

Abstract

It is demonstrated that the side-chain engineering of polymer donors and molecular conformation of small-molecule acceptors (SMAs) plays a crucial role in the morphology and photovoltaic performance of polymer solar cells (PSCs). However, the synergetic effect of these two aspects has been rarely reported. Herein, two wide-band gap donor−acceptor (D−A) copolymers (PST-TTC and PSPT-TTC) featuring the same main-chain backbone but different conjugated side chains were developed and combined with three low-band gap symmetric SMAs (ITIC, DTCFO-ICCl, and Y6) with various molecular conformations (Sshape, C-shape, and U-shape) to investigate the synergetic effect of side-chain engineering of polymer donors and conformation manipulation of SMAs on molecular properties, device physics, film morphology, and photovoltaic performance. The results indicate that PST-TTC with an alkylthiothiophene side chain exhibits a broader absorption spectrum, a smaller optical band gap (1.95 vs 1.99 eV), and a deeper-lying highest occupied molecular orbital (HOMO) level (−5.39 vs −5.36 eV) as compared to PSPT-TTC with an alkylthiophenylthiophene side chain. The PSCs were constructed according to the different donor/acceptor combinations based on the two as-synthesized polymers and three selected SMAs. After optimization, PST-TTC paired with Sshaped ITIC provides a power conversion efficiency (PCE) of 10.10% and the PCE can be further improved up to 10.60% when Cshaped DTCFO-ICCl was used to replace ITIC as the acceptor. However, the device performance becomes worse, accompanied with a sharply reduced PCE of 7.36% after the substitution of ITIC for U-shaped Y6. On the contrary, when the paired donor was changed to PSPT-TTC, the PSPT-TTC:Y6-based PSC achieves a remarkably increased PCE of up to 11.46%. These delicate observations suggest that the polymer donor with different conjugated side chains should collaborate with symmetric SMAs possessing various molecular conformations to realize superior morphology and device performance.

Molecular engineering of N,S-heteroarene-based small-molecule acceptors: effects of side chains, backbone extension and end groups on structure, optoelectronic properties and solar cell performance

“…The different molecular geometry should stem from the fact that the S atoms from thiophene ends in the NIT-based pentacyclic or hexacyclic central core can form intramolecular noncovalent interactions with O atoms from IC or ICF, which can afford a planar backbone structure. 45–49 Although three acceptors of T-NIT68 , NIT810-T , and NIT810-T-F possess the same molecular geometry, their specific molecular and electronic structures are different. The orientation of the bulky alkyl chain (2-hexyldecyl) on the N atom and CO group in the terminal IC unit of T-NIT68 is on the same side, whereas for NIT810-T and NIT810-T-F , the two parts are on opposite sides.…”

A Review on Solution-Processed Organic Phototransistors and Their Recent Developments

“…This solution-processable conjugated polymer showed a high D* value of more than 2.1 × 10 9 Jones. Most recently, Li et al [126] synthesised and tested two benzo[1,2-b:4,5-b ]dithiophene (BDT) and 2,2 :5 ,2 -terthiophene-3,3 -dicarboxylate (TTC) based polymers; PST-TTC and PSPT-TTC with three different small molecule acceptors (ITIC/S shape, DTCFO-ICCI/C shape, and Y6/U shape) to examine their photovoltaic performances. PST and PSPT had different conjugated side chains of alkylthiothiophene (ST) and alkylthiophenylthiophene (SPT) on the BTT unit.…”

A Light Soaking Free Solution Processable Metal Oxide Cathode Interfacial Layer Enables High Efficiency in Bulk Heterojunction Polymer Solar Cells

“…Owing to the encouraging progress on PSCs in the past decade, the power conversion efficiency (PCE) has been improved over 18% with non-fullerene BHJ based systems . The pathways employed to achieve maximum efficiency include introducing the new electron donor, non-fullerene acceptor, good charge carrier interfacial layer material, and morphology control. − New charge transport interfacial materials have significantly improved the efficiency and stability of the organic solar cell (OSC) devices. So far, various charge transport layers including ionic liquids, zwitterionic molecules, alkali salts, n-type metal oxides such as TiO x , − ZnO, SnO x , Al doped ZnO, Mg doped ZnO, neutral polymers (e.g., PEIE), and conjugated polyelectrolytes (e.g., PFN) have been introduced to improve both the stability and power conversion efficiency of PSC devices.…”