Issue 21, 2023

Unraveling the origin of improved photovoltaic performance in acceptor–acceptor-structured perylene-diimide-based polymeric acceptors through partially fluorinating benzo[c][1,2,5]thiadiazole

Abstract

Recently, perylene diimide (PDI)-based all-polymer solar cells (All-PSCs) have gained increasing attention due to molecular structural diversity, facile chemical modification, and mechanical and morphological stability. However, acceptor–acceptor (A–A)-structured PDI-based polymeric acceptors (PAs) exhibit inferior photovoltaic performance to donor–acceptor type and/or fused-PDI-based ones. Herein, two A–A type thermo- and photo-stable PAs, namely, PPDI-DTBT and PPDI-DTFBT, by choosing a long 2-octyldodecyl-substituted PDI unit and 4,7-dithienylbenzo[c][1,2,5]thiadiazole (DTBT) and/or partially fluorinated 4,7-dithienyl-5-fluorobenzo[c][1,2,5]thiadiazole (DTFBT) subunits to construct a polymer backbone, were developed. Both of them possess a complementary absorption profile and a similar ELUMO to donor PTB7-Th. Not only a slightly descended LUMO energy level, better molecular planarity and aggregation, and reduced exciton binding energy (Eb), but also enhanced exciton dissociation efficiency, more closed and ordered stacking, higher and balanced charge mobility and a desired microstructural morphology structure were achieved in partially fluorinated PPDI-DTFBT. Moreover, femtosecond transient absorption (fs-TA) spectra suggested faster and more efficient exciton dissociation and transfer characteristics in the PTB7-Th:PPDI-DTFBT system. These changes enabled the PPDI-DTFBT-based device to acquire a PCE of 6.04%, which was 51.76% higher than that (3.98%) of its counterpart. This increase was mainly profited from 32.70% increased JSC from 11.10 to 14.73 mA cm−2 and 13.92% enhanced FF from 46.54% to 53.02%. The current results demonstrate that precisely incorporating fluorine into an A–A type PDI-based polymer backbone can synergistically adjust the molecular aggregation and improve the photophysical process, with the aim of gaining an inspirational device efficiency in all-PSCs.

Graphical abstract: Unraveling the origin of improved photovoltaic performance in acceptor–acceptor-structured perylene-diimide-based polymeric acceptors through partially fluorinating benzo[c][1,2,5]thiadiazole

Supplementary files

Article information

Article type
Paper
Submitted
25 Feb 2023
Accepted
20 Apr 2023
First published
21 Apr 2023

J. Mater. Chem. C, 2023,11, 6951-6962

Unraveling the origin of improved photovoltaic performance in acceptor–acceptor-structured perylene-diimide-based polymeric acceptors through partially fluorinating benzo[c][1,2,5]thiadiazole

J. Tong, W. Liu, Y. Huang, Z. Li, Y. Wang, S. Bai, Z. Liang, L. Yan, J. Li and Y. Xia, J. Mater. Chem. C, 2023, 11, 6951 DOI: 10.1039/D3TC00696D

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