Issue 44, 2018

Aromatic end-capped acceptor effects on molecular stacking and the photovoltaic performance of solution-processable small molecules

Abstract

Aromatic end-capped acceptors are important in constructing donor materials and non-fullerene acceptors in organic solar cells. However, their features (such as electron-withdrawing ability and subtle change in planarity) and effects on molecular stacking and photovoltaic performance, lack a systematic study. This manuscript reports four molecules, namely, BT-RCN, BT-BA, BT-RA, and BT-ID, which are terminated by different acceptors in the same backbone. We quantify the molecular planarity through their dipole moment in the Z direction and investigate the effect of the degree of planarity on molecular properties and device performances. The four acceptors are classified into two groups based on acceptor strength: medium-strong and strong acceptors. Molecules based on medium-strong acceptors exhibit excellent efficiencies as follows: 10.1% for BT-ID, 9.6% for BT-RA, and 8.5% for BT-BA. Their decreased efficiency is quite consistent with their lowered hole mobility. Grazing incidence X-ray diffraction results demonstrate the positive relationship between the non-planarity of the acceptors and d-spacing distance in the π–π stacking direction, which are detrimental to mobility. BT-RCN, with a strong acceptor, obtains the lowest efficiency of 6.1%. These findings indicate the importance of matching the electron-donating ability of donor units and electron-withdrawing ability of acceptor units, and the subtle planarity change in molecular properties and aggregation.

Graphical abstract: Aromatic end-capped acceptor effects on molecular stacking and the photovoltaic performance of solution-processable small molecules

Supplementary files

Article information

Article type
Paper
Submitted
03 May 2018
Accepted
08 Jun 2018
First published
15 Jun 2018

J. Mater. Chem. A, 2018,6, 22077-22085

Aromatic end-capped acceptor effects on molecular stacking and the photovoltaic performance of solution-processable small molecules

D. Deng, Y. Yang, W. Zou, Y. Zhang, Z. Wang, Z. Wang, J. Zhang, K. Lu, W. Ma and Z. Wei, J. Mater. Chem. A, 2018, 6, 22077 DOI: 10.1039/C8TA04102D

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