Fine structural design and configuration regulation of DPP-based organic small molecule photovoltaic donors

Abstract

A series of six DPP-based organic small molecule photovoltaic donor materials were designed and synthesized successfully. The targeted structural design and regulation of the materials were carried out in three steps. Firstly, the introduction of a π-bridge in the molecule enhances the intramolecular charge transfer (ICT) effect and improves the short-circuit current (J_sc) of the device. Secondly, different end groups were introduced to adjust the energy levels of molecules, to obtain more matching donor materials for acceptor materials. Finally, the molecular configuration was adjusted to meet the requirements of increasing the open circuit voltage (V_oc). It is worth mentioning that for the end group regulation strategy, a small molecule donor was synthesized, in which fluorene-capped triarylamine as the electron-donating unit provided a reference for the future development of related donor materials. To our knowledge, the selection of triphenylamine and phenyl-carbazole as central nuclei for double-armed small molecule donors has been rarely reported. In this work, triphenylamine and phenyl-carbazole were used as the central nuclei of the A–π–D–π–A type molecular configuration, resulting in lower HOMO energy levels and higher V_oc. As a result, without further optimization of the devices, the power conversion efficiency (PCE) of the photovoltaic device based on (DPP)₂TPA was more than three times that of a previously reported device based on TPA-DPP-TPA, and the PCE of the device based on (DPP)₂PCZ was more than twice that of a previously reported device based on SM1. Our work demonstrates that optimization of photovoltaic performance can be achieved through rational structural design and configuration regulation of the photovoltaic material, which provides important guidance for the development of novel photovoltaic materials in the future.