CC BY-NC-ND 4.0 · Organic Materials 2021; 03(02): 134-140
DOI: 10.1055/s-0041-1726427
Focus Issue: Peter Bäuerle 65th Birthday
Original Article

Efficient Solar Cells Based on a Polymer Donor with β-Branching in Trialkylsilyl Side Chains

a  Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
Martijn M. Wienk
a  Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
a  Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
b  Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands
› Author Affiliations


Side-chain engineering is an important strategy in designing novel polymer semiconductor materials for high-efficient organic solar cells. The use of trialkylsilyl side chains can improve the photovoltaic efficiency by decreasing the energy of the HOMO of the polymer and improving its crystallinity and hole mobility. Compared to simple linear derivatives, α-branching in the alkyl groups of trialkylsilyl side chains causes strong aggregation and excessive phase separation in the photoactive layer, leading to poor device performance. β-Branching of the alkyl groups has not yet been used in trialkylsilyl side chains. Herein, we describe a new polymer (J77) with triisobutylsilyl side chains to investigate the effect of β-branching on the molecular aggregation, optical properties, energy levels, and photovoltaic properties. We find that compared to α-branching, β-branching of alkyl groups in trialkylsilyl side chains significantly reduces aggregation. This enables J77 to form blend morphologies in films that provide high-efficient solar cells in combination with different non-fullerene acceptors. Moreover β-branching of the alkyl groups in trialkylsilyl side chains lowers the HOMO energy level of J77 and increases the open-circuit voltage of J77-based solar cells without sacrificing short-circuit current density or fill factor.

Supporting Information

Supporting Information for this article is available online at

Dedicated to Professor Peter Bäuerle on the occasion of his 65th birthday.

Supporting Information

Publication History

Received: 15 January 2021

Accepted: 24 February 2021

Publication Date:
01 April 2021 (online)

© 2021. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (

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