Small-molecule acceptors based on 4H-cyclopenta[1,2-b:5,4-b′]dithiophene units with near-infrared absorption for nonfullerene polymer solar cells

Simple near-Infrared Nonfullerene Acceptors Enable Organic Solar Cells with >9% Efficiency

“…Moreover, similar to IDT and its derivatives, CPDT’s rigid ring-fused structure and orthogonal side chains can guarantee both high carrier mobility and good solubility that enable the solution process. Therefore, attempts have been made to introduce CPDT into the π-conjugate backbone of NFA to extend its light absorbance to the NIR region. − Recently, PCE records over 11% have been made by CPDT-based low bandgap ( E gap ≈ 1.55 eV) NFA via reasonable molecular engineering, yet the NIR NFAs derived from CPDT still exhibited moderate photovoltaic performance with PCE merely surpassed 8% …”

“…In 2017, Tang et al reported a new NFA named 2CIC that contains a dimerized CPDT as an electron-donating core and 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)­malononitrile (INCN) as electron-accepting end-groups . Although its photovoltaic performance was relatively low (PCE = 3.5%), Tang et al proposed a new strategy to design NFAs with strong NIR absorption through facile synthesis.…”

Effects of Electron-Donating and Electron-Accepting Substitution on Photovoltaic Performance in Benzothiadiazole-Based A–D–A′–D–A-Type Small-Molecule Acceptor Solar Cells

“…On the basis of the considerations described above, herein, we have designed and synthesized three A–D–A′–D–A-type NFRAs ( BTCPDT , BTCPDTO4 , and BTCPDTF ), in which two cyclopentadithiophene (CPDT) units and one benzo­[ c ]­[1,2,5] thiadiazole (BT) unit is used as D–A′–D with two A units, 2-(5,6-difluoro-3-oxo-2,3-dihydro-1 H -inden-1-ylidene) malononitrile (2FID). The CPDT is a multiple-ring electron-rich moiety with a strong electron-donating ability. − In addition, BT is one of the most commonly used acceptor moieties in low band gap organic semiconductors. , In particular, the CPDT–BT unit has been widely used as a polymer donor because of its near-infrared absorbing property ascribed to a strong push–pull effect between CPDT and BT. − Furthermore, they cross each other at the centered BT and thereby offer an advantage for intermolecular π–π stacking for high charge transport ability . In addition, 2FID was used as a strong electron deficient end group to enhance the ICT effect, which results in red-shifted absorption and a strong extinction coefficient. , In this study, alkoxy and fluorine groups were introduced to the 5,6-position of the BT to investigate the effects of electron-donating and electron-accepting substitutions in the A′ core on the optoelectronic, morphological, and photovoltaic properties of the A–D–A′–D–A-type NFRA-based OSCs.…”

TTA as a potential hole transport layer for application in conventional polymer solar cells

“…However, few studies on employing small molecules as an independent HTL in the fabrication of OSC devices were reported. http://engine.scichina.com/doi/10.1016/j.jechem.2019.07.005 Solution-processed small molecules have gained considerable attention because of their self-dependent molecular structures, comparatively high-degree purity and good repeatability in contrast with polymers, which allows for the application in the field of organic solar cells [27,28] . Taking all the above into consideration, the introduction of a well-designed novel small molecule as the replacement of PEDOT:PSS is appealing.…”