Issue 30, 2024

The effect of rigid-block length in elastomer-containing photoactive block copolymers on the photovoltaic and mechanical properties of polymer solar cells

Abstract

Organic solar cells (OSCs) used in wearable devices should exhibit mechanical robustness in addition to high power conversion efficiencies (PCEs). Achieving this goal involves integrating polymer donors (PDs) with elastomers via block copolymerization. However, the underlying design principles, particularly the effect of block length within the PD-elastomer block copolymers (BCPs), are not well understood. In this work, we synthesize three D18-b-poly(dimethylsiloxane) (PDMS) BCPs with different block lengths—namely, D18L-b-PDMS, D18M-b-PDMS, and D18H-b-PDMS—by varying the numberaverage molecular weight (Mn = 8.6, 14.4, and 22.6 kg mol−1, respectively) of the D18 conjugated segments. An increase in the Mn of the D18 blocks leads to the formation of distinct crystalline structures in the photoactive layer, which facilitates charge transport and diminishes charge recombination in OSCs. Consequently, the PCE of OSCs is improved from D18L-b-PDMS (15.1%), to D18M-b-PDMS (16.4%), and to D18H-b-PDMS (17.3%). The presence of PDMS segments in the D18x-b-PDMS BCPs increases the degree of polymer-chain entanglement, resulting in the high toughness (>1.8 MJ m−3) of D18x-b-PDMS:L8-BO blend films. Therefore, the OSCs based on these BCPs not only achieve PCEs (15.1–17.3%) that surpass those of the OSCs based on random copolymers (PCE = 12.30%) but also exhibit mechanical robustness (toughness = 1.8–2.6 MJ m−3) exceeding those of the OSCs based on the reference D18 (toughness = 0.5 MJ m−3) and D18:PDMS physical blends (PCE = 8.60% and toughness = 0.1 MJ m−3). Thus, this study demonstrates the effectiveness of the PD-elastomer BCP design and underscores the significance of controlling the molecular weight of the block segments within the BCPs for simultaneously achieving high photovoltaic efficiency and mechanical properties in OSCs.

Graphical abstract: The effect of rigid-block length in elastomer-containing photoactive block copolymers on the photovoltaic and mechanical properties of polymer solar cells

Supplementary files

Article information

Article type
Paper
Submitted
09 Apr 2024
Accepted
14 Jun 2024
First published
17 Jun 2024

J. Mater. Chem. A, 2024,12, 19039-19051

The effect of rigid-block length in elastomer-containing photoactive block copolymers on the photovoltaic and mechanical properties of polymer solar cells

H. Lee, J. Lee, E. S. Oh, M. J. Lee, T. Kim, C. Lee and B. J. Kim, J. Mater. Chem. A, 2024, 12, 19039 DOI: 10.1039/D4TA02429J

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