Jump to main content
Jump to site search

Issue 33, 2017
Previous Article Next Article

Low band gap conjugated polymers combining siloxane-terminated side chains and alkyl side chains: side-chain engineering achieving a large active layer processing window for PCE > 10% in polymer solar cells

Author affiliations

Abstract

Alternating and random conjugated copolymers with a siloxane-terminated side chain for a repeating unit based on 5,6-difluoro[2,1,3]benzothiadiazole (FBT) and quarterthiophene (4T) were synthesized, among which side-chain random copolymers PFBT4T-C5Si-50% and PFBT4T-C5Si-25% with low contents of 50% and 25% siloxane-terminated side chains, respectively, in conjunction with alkyl side chains were found to be more suitable for optoelectronic applications due to good film-forming in solution processing. Grazing incidence X-ray diffraction (GIXD) indicated that the siloxane-terminated side chain could induce PFBT4T-C5Si-50% and PFBT4T-C5Si-25% with face-on orientations, giving high 3-D hole transport in neat films as supported by a high hole mobility up to 2.46 cm2 V−1 s−1 in field-effect transistors and an SCLC hole mobility up to 5.9 × 10−2 cm2 V−1 s−1 in hole-only devices. Fast SCLC hole and electron transports were seen for their bulk-heterojunction (BHJ) blend films with PC71BM as the acceptor, due to the retention of a polymer face-on orientation. The BHJ blend film of PFBT4T-C5Si-25% showed lower film surface roughness, more balanced hole and electron transport, and relatively smaller phase separation when compared with PFBT4T-C5Si-50%, as evidenced by atomic force microscopy (AFM), transmission electron microscopy (TEM), SCLC, and resonant soft X-ray scattering (RSoXS) measurements. The PFBT4T-C5Si-25%-based PSCs with 270, 420, and 600 nm thick active layers exhibited outstanding power conversion efficiencies (PCEs) of 10.39%, 11.09%, and 10.15%, respectively, readily offering a high thickness tolerance to achieve an unprecedented wide active layer processing window for PCE > 10%. This is also the first PCE of more than 10% achieved by an active layer of a 600 nm thickness level in PSCs. Another notable feature is very high fill factors of more than 74% and 71% being achieved for very thick active layers of 420 and 600 nm, respectively. The results suggest that side-chain engineering through the incorporation of a partial siloxane-terminated side chain is a unique handle to afford new photovoltaic polymers with enhanced vertical carrier transport towards application in roll-to-roll processing of PSCs.

Graphical abstract: Low band gap conjugated polymers combining siloxane-terminated side chains and alkyl side chains: side-chain engineering achieving a large active layer processing window for PCE > 10% in polymer solar cells

Back to tab navigation

Supplementary files

Publication details

The article was received on 27 Jun 2017, accepted on 24 Jul 2017 and first published on 25 Jul 2017


Article type: Paper
DOI: 10.1039/C7TA05583H
Citation: J. Mater. Chem. A, 2017,5, 17619-17631
  •   Request permissions

    Low band gap conjugated polymers combining siloxane-terminated side chains and alkyl side chains: side-chain engineering achieving a large active layer processing window for PCE > 10% in polymer solar cells

    X. Liu, L. Nian, K. Gao, L. Zhang, L. Qing, Z. Wang, L. Ying, Z. Xie, Y. Ma, Y. Cao, F. Liu and J. Chen, J. Mater. Chem. A, 2017, 5, 17619
    DOI: 10.1039/C7TA05583H

Search articles by author

Spotlight

Advertisements