Theoretical Design of Dithienopicenocarbazole-Based Molecules by Molecular Engineering of Terminal Units Toward Promising Non-fullerene Acceptors.

Jie Feng,Youyong Li,Hongshuai Wang,Nopporn Rujisamphan

doi:10.3389/fchem.2020.580252

Abstract

Dithienopicenocarbazole (DTPC), as the kernel module in A-D-A non-fullerene acceptors (NFA), has been reported for its ultra-narrow bandgap, high power conversion efficiency, and extremely low energy loss. To further improve the photovoltaic performance of DTPC-based acceptors, molecular engineering of end-capped groups could be an effective method according to previous research. In this article, a class of acceptors were designed via bringing terminal units with an enhanced electron-withdrawing ability to the DTPC central core. Their geometrical structures, frontier molecular orbitals, absorption spectrum, and intramolecular charge transfer and energy loss have been systematically investigated on the basis of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Surprisingly, NFA 4 highlights the dominance for its increased open circuit voltages while NFA 2, 7, and 8 exhibit great potential for their enhanced charge transfer and lower energy loss, corresponding to a higher short-circuit current density. Our results also manifest that proper modifications of the terminal acceptor with extensions of π-conjugation might bring improved outcomes for overall properties. Such a measure could become a feasible strategy for the synthesis of new acceptors, thereby facilitating the advancement of organic solar cells.

Highlights

Organic solar cells (OSCs), recognized for their great potential as sustainable energy sources, have been attracting extensive attention from researchers (Brabec et al, 2001; Gao et al, 2018; Upama et al, 2020; Zhao et al, 2020)
The absorption spectrum of investigated non-fullerene acceptors (NFA) were simulated by TD-density functional theory (DFT)/CAM-B3LYP under the solvent condition of dichloromethane with polarizable continuum model (PCM), as CAM-B3LYP (19% HFexc at short-range and 65% HFexc at long-range) was proven to be a valid function that could exactly take the effect of charge transfer into account (Gross and Kohn, 1985; Yanai et al, 2004)
The dihedral angles and bond lengths between the DTPC core and end-capped acceptor are listed in Supplementary Table 2

Summary

Introduction

Organic solar cells (OSCs), recognized for their great potential as sustainable energy sources, have been attracting extensive attention from researchers (Brabec et al, 2001; Gao et al, 2018; Upama et al, 2020; Zhao et al, 2020). Dithienopicenocarbazole as Non-fullerene Acceptors of fullerene derivatives, there still remain several troublesome obstacles to be overcome, such as complex synthesis, week absorption abilities, poor light harvesting properties, and hardly tunable band gaps (Liang and Yu, 2010; Lin et al, 2012; Chen et al, 2015). The above difficulties have given birth to non-fullerene acceptor materials, which offer several unique advantages, including low-cost facile synthesis, tunable flexibility of FMO energy levels, and superior capacity of light absorption in the visible region (Anthony, 2011; Ala’a et al, 2014; Li et al, 2015a; Lin et al, 2015). Researchers are still persisting in advancing progress in the research of non-fullerene acceptors (NFA)

Methods

Results

Conclusion