9,9′‐Bifluorenylidene‐Core Perylene Diimide Acceptors for As‐Cast Non‐Fullerene Organic Solar Cells: The Isomeric Effect on Optoelectronic Properties

Abstract

Two different non-fullerene small-molecule acceptors, m-PIB and p-PIB, based on 9,9'-bifluorenylidene (BF) and perylene diimide (PDI) were designed and synthesized. Four β-substituted PDIs were linked to BF in different positions. Based on DFT analysis, derivative p-PIB exhibited reduced intramolecular twisting between the PDI moieties, more delocalized wave function, and sufficiently wider π-electron delocalization than that of m-PIB. The absorption ability of p-PIB was enhanced due to increased intermolecular interactions. By blending p-PIB with poly{4,8-bis[5-(2ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene-co-3-fluorothieno[3,4-b]-thiophene-2-carboxylate} (PTB7-Th), organic solar cells (OSCs) based on p-PIB obtained a maximum power conversion efficiency of 5.95 % without any treatments. Due to the improved and balanced hole and electron mobilities, the short-circuit current and fill factor of OSCs based on PTB7-Th and p-PIB were significantly increased. The AFM and TEM results revealed that the PTB7-Th:p-PIB film had favorable nanoscale phase separation and formed a bicontinuous interpenetrating network.

Effects of Different Ring‐Expanded Strategies for Nonfullerene Acceptors in Organic Photovoltaics under Donor and Acceptor Excitation

“…B3LYP has been confirmed to reasonably evaluate the geometric and electronic properties of 99′BF derivatives [20c,24] . As for the absorption spectra and excited states, B3LYP with 6‐31G(d) basis set was utilized using time‐dependent density functional theory (TD‐DFT) based on the optimized ground‐state structures [21b] . The internal conversion rate ( k ic ), radiative rate ( k r ), and intersystem crossing rate ( k isc ) were calculated by the MOMAP (Molecular Materials Property Prediction Package) program.…”

Isomerization Strategy of Nonfullerene Small‐Molecule Acceptors for Organic Solar Cells

“…Our group designed two PDI tetramers, namely, m-PIB and p-PIB, where the β-substituted PDIs were linked to the 9,9′-bifluorenylidene core at different places. [90] DFT analysis tells that p-PIB displayed declined intramolecular twist between the PDI moieties, more deviated wave function, and wider π electron delocalization than m-PIB, which leads to the stronger absorption ability of p-PIB. OSCs based on PTB7-Th:p-PIB afford a PCE of 5.95% with an open-circuit voltage (V OC ) of 0.82 V, a short-circuit current density (J SC ) of 12.32 mA cm −2 , and a fill factor (FF) of 58.72%, exceeding its PTB7-Th:m-PIB counterparts (4.27%).…”

Star‐Shaped Non‐Fullerene Small Acceptors for Organic Solar Cells

“…Moreover, the p ‐PIB film showed a more balanced hole and electron mobility. Finally, the OSC based on p ‐PIB exhibited a PCE of 5.95 % without any treatments …”