Thiophene Rings Improve the Device Performance of Conjugated Polymers in Polymer Solar Cells with Thick Active Layers

Abstract

Developing novel materials that tolerate thickness variations of the active layer is critical to further enhance the efficiency of polymer solar cells and enable large‐scale manufacturing. Presently, only a few polymers afford high efficiencies at active layer thickness exceeding 200 nm and molecular design guidelines for developing successful materials are lacking. It is thus highly desirable to identify structural factors that determine the performance of semiconducting conjugated polymers in thick‐film polymer solar cells. Here, it is demonstrated that thiophene rings, introduced in the backbone of alternating donor–acceptor type conjugated polymers, enhance the fill factor and overall efficiency for thick (>200 nm) solar cells. For a series of fluorinated semiconducting polymers derived from electron‐rich benzo[1,2‐b:4,5‐b′]dithiophene units and electron‐deficient 5,6‐difluorobenzo[2,1,3]thiazole units a steady increase of the fill factor and power conversion efficiency is found when introducing thiophene rings between the donor and acceptor units. The increased performance is a synergistic result of an enhanced hole mobility and a suppressed bimolecular charge recombination, which is attributed to more favorable polymer chain packing and finer phase separation.

Electron Acceptors With a Truxene Core and Perylene Diimide Branches for Organic Solar Cells: The Effect of Ring-Fusion

“…The HOMO/LUMO levels are −6.09/−3.64 eV for Tr-3PDI and −6.11/−3.44 eV for FTr-3PDI, respectively. The slightly up-shifted LUMO level of FTr-3PDI will help to offer a higher open-circuit voltage ( V oc ), and the down-shifted HOMO level is favorable for hole transfer from excited acceptor phase to donor phase in BHJ OSCs (Duan et al, 2016a , 2017b , 2018 ; Jia et al, 2017 ).…”

A Wide‐Bandgap Conjugated Polymer Based on Quinoxalino[6,5‐f ]quinoxaline for Fullerene and Non‐Fullerene Polymer Solar Cells

“…In this work, we developed a new conjugated polymer PNQx‐2F2T ( Scheme ) based on DTNQx by choosing 3,3 ' ‐difluoro‐2,2 ' ‐bithiophene (2F2T) as the co‐monomer. Compared to BDTT, 2F2T is much smaller in size as it does not contain bulky side chains, which will allows for closer alkyl‐alkyl interdigitation and more ordered interchain lamellar stacking for the resulting polymer . Besides, the electron‐withdrawing fluorine atoms on 2F2T can not only deepen the highest occupied molecular orbital (HOMO) of the polymers but also induce non‐covalent attractive interactions between the hydrogen or sulfur atoms (H…F or S…F), which may contribute to the enhancement of V oc , and coplanarity of the polymer backbone and polymer crystallinity, respectively .…”

Alternative Thieno[3,2‐b][1]benzothiophene Isoindigo Polymers for Solar Cell Applications

“…Organic photovoltaics have seen a rapid increase in performance in recent years with efficiencies over 13% being reported . This resurgence in efficiency has been lead primarily through new molecular design and efficient morphological control of both donor and acceptor . The importance of morphology for high efficiency organic photovoltaics has been highlighted many times, an optimized interpenetrating network of the two components is needed for efficient exciton dissociation.…”