Design Principles and Synergistic Effects of Chlorination on a Conjugated Backbone for Efficient Organic Photovoltaics: A Critical Review

Abstract

The pursuit of low‐cost, flexible, and lightweight renewable power resources has led to outstanding advancements in organic solar cells (OSCs). Among the successful design principles developed for synthesizing efficient conjugated electron donor (ED) or acceptor (EA) units for OSCs, chlorination has recently emerged as a reliable approach, despite being neglected over the years. In fact, several recent studies have indicated that chlorination is more potent for large‐scale production than the highly studied fluorination in several aspects, such as easy and low‐cost synthesis of materials, lowering energy levels, easy tuning of molecular orientation, and morphology, thus realizing impressive power conversion efficiencies in OSCs up to 17%. Herein, an up‐to‐date summary of the current progress in photovoltaic results realized by incorporating a chlorinated ED or EA into OSCs is presented to recognize the benefits and drawbacks of this interesting substituent in photoactive materials. Furthermore, other aspects of chlorinated materials for application in all‐small‐molecule, semitransparent, tandem, ternary, single‐component, and indoor OSCs are also presented. Consequently, a concise outlook is provided for future design and development of chlorinated ED or EA units, which will facilitate utilization of this approach to achieve the goal of low‐cost and large‐area OSCs.

Engineering the Core Units of Small‐Molecule Acceptors to Enhance the Performance of Organic Photovoltaics

“…In addition to balanced charge mobility, the FF is also closely correlated to the bimolecular recombination rate in BHJ films. [ 36 ] Furthermore, balanced charge carrier mobilities in the devices would minimize the charge accumulation effect, consistent with the greater value of J SC for the PTQ10:Y7 BHJ OPV.…”

Tetrabromination versus Tetrachlorination: A Molecular Terminal Engineering of Nonfluorinated Acceptors to Control Aggregation for Highly Efficient Polymer Solar Cells with Increased Voc and Higher Jsc Simultaneously

“…To further understand the carrier transport properties of these PSCs, the mobilities ( μ h and μ e ) of PM6:TSeIC4Cl and PM6:TSeIC4Br blend films and neat films of two NF‐SMAs were measured by space‐charge‐limited‐current (SCLC) method (Figure S4, Supporting Information, and Figure ). The electron mobilities of neat films TSeIC4Cl and TSeIC4Br are 7.4 × 10 − 4 cm 2 (V s) − 1 and 7.9 × 10 − 4 cm 2 (V s) − 1 , respectively, indicating TSeIC4Br shows higher mobility than TSeIC4Cl . For blends, the PM6:TSeIC4Cl blend film exhibits a hole mobility of 7.49 × 10 − 4 cm 2 (V s) − 1 and an electron mobility of 3.82 × 10 − 4 cm 2 (V s) − 1 .…”

“…The electron mobilities of neat films TSeIC4Cl and TSeIC4Br are 7.4 × 10 − 4 cm 2 (V s) − 1 and 7.9 × 10 − 4 cm 2 (V s) − 1 , respectively, indicating TSeIC4Br shows higher mobility than TSeIC4Cl . For blends, the PM6:TSeIC4Cl blend film exhibits a hole mobility of 7.49 × 10 − 4 cm 2 (V s) − 1 and an electron mobility of 3.82 × 10 − 4 cm 2 (V s) − 1 . As for the PM6:TSeIC4Br blend film, the μ h and μ e are 7.61 × 10 − 4 cm 2 (V s) − 1 and 4.21 × 10 − 4 cm 2 (V s) − 1 .…”

“…For blends, the PM6:TSeIC4Cl blend film exhibits a hole mobility of 7.49 × 10 − 4 cm 2 (V s) − 1 and an electron mobility of 3.82 × 10 − 4 cm 2 (V s) − 1 . As for the PM6:TSeIC4Br blend film, the μ h and μ e are 7.61 × 10 − 4 cm 2 (V s) − 1 and 4.21 × 10 − 4 cm 2 (V s) − 1 . Therefore, PM6:TSeIC4Cl and PM6:TSeIC4Br‐ based PSCs have the μ h / μ e ratios of 1.96 and 1.81, respectively.…”

“…Polymer solar cells (PSCs) have achieved a huge breakthrough in the past 5 years with the combinational contributions from the developments of nonfullerene acceptors (NFAs), polymeric donors, and kind of redundant of device engineering. [ 1–12 ] Compared with traditional fullerene acceptors, A–D–A framework nonfullerene small molecular acceptors (NF‐SMAs) have significant advantages in broader absorption range, tunable molecular structure and energy levels, and diversified donor materials for matching. [ 13–23 ] Therefore, many such typed NF‐SMAs have been synthesized and become the mainstream materials for the development of high‐efficiency PSCs.…”