Fluorinated Photovoltaic Materials for High‐Performance Organic Solar Cells

Abstract

Over the past decade, organic solar cells (OSCs) have achieved a dramatic boost in their power conversion efficiencies from about 6 % to over 16 %. In addition to developments in device engineering, innovative photovoltaic materials, especially fluorinated donors and acceptors, have become the dominant factor for improved device performance. This minireview highlights fluorinated photovoltaic materials that enable efficient OSCs. Impressive OSCs have been obtained by developing some important molds of fluorinated donor and acceptor systems. The molecular design strategy and the matching principle of fluorinated donors and acceptors in OSCs are discussed. Finally, a concise summary and outlook are presented for advances in fluorinated materials to realize the practical application of OSCs.

Bromination: An Alternative Strategy for Non‐Fullerene Small Molecule Acceptors

“…Halogenation is an effective strategy used to increase the optical absorption, refine the energy levels, and improve the molecular packing of semiconductor materials. [ 19–22 ] Numerous studies [ 23–29 ] have reported on the use of fluorine in OSCs materials and have indicated that the small atom size of fluorine provides the highest electronegativity, leading to the modulation of the π‐electron properties. [ 30,31 ] More recently, chlorinated materials have emerged as a promising alternative in the field of solar energy.…”

Over 15% Efficiency Polymer Solar Cells Enabled by Conformation Tuning of Newly Designed Asymmetric Small‐Molecule Acceptors

“…Non‐fullerene small‐molecule acceptors (SMAs) have been taken as the mainstream of researches for their great potential of reaching high power conversion efficiencies (PCEs) and stabilities. [ 7–12 ] Currently, the PCEs of the state‐of‐the‐art non‐fullerene SMA based PSCs have already surpassed 16% derived from the PM6: Y6 system reported by Zou et al [ 13–20 ]…”

Optimized Active Layer Morphologies via Ternary Copolymerization of Polymer Donors for 17.6 % Efficiency Organic Solar Cells with Enhanced Fill Factor

“…At present, the further increase of PCE needs to optimize all relevant photovoltaic parameters of OSCs, including the open‐circuit voltage ( V oc ), short‐circuit current density ( J sc ), and fill factor (FF). In general, the V oc is mainly governed by the molecular frontier orbital energy levels, i.e., the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, and the J sc is mainly dominated by the absorption capability of the active layer, and both of them have been extensively well studied and achieved great successes through systematic design of photovoltaic materials [1, 31, 32] . On the other hand, the FF as an equally important third parameter in determining PCE, which is more sensitive and determined by comprehensive and complicated courses, including charge generation, transport, recombination, and extraction, is still a challenging issue [33–36] …”

“…Thus, to fully explore the photovoltaic potential of PM6 in OSCs, finely regulating the molecular structure to further optimize the corresponding active layer morphologies is of considerable significance. Although some molecular design strategies of polymer donors have been successfully implemented to achieve better the trade‐off among the V oc , J sc , and FF, such as heteroatom substitutions, [22a, 32, 45–47] side‐chain engineering, [41b, 48] and terpolymerization, [44, 49–51] further extensive studies are still necessary to in‐depth understand the reasons behind them.…”

“…In general, the V oc is mainly governed by the molecular frontier orbital energy levels,i.e., the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels,a nd the J sc is mainly dominated by the absorption capability of the active layer, and both of them have been extensively well studied and achieved great successes through systematic design of photovoltaic materials. [1,31,32] On the other hand, the FF as an equally important third parameter in determining PCE, which is more sensitive and determined by comprehensive and complicated courses,i ncluding charge generation, transport, recombination, and extraction, is still ac hallenging issue. [33][34][35][36] So far,toboost the FF of OSCs,alot of works have been focused on device engineering to simultaneously improve the corresponding charge generation, transport and extraction, as well as reduce charge recombination, including the modification of interlayer [17,28,30,37] and the optimization of bulk heterojunction (BHJ) active layer morphologies.…”