Eco-Friendly Solvent-Processed Dithienosilicon-Bridged Carbazole-Based Small-Molecule Acceptors Achieved over 25.7% PCE in Ternary Devices under Indoor Conditions

Abstract

Terminal acceptor atoms and side-chain functionalization play a vital role in the construction of efficient nonfullerene small-molecule acceptors (NF-SMAs) for AM1.5G/indoor organic photovoltaic (OPV) applications. In this work, we report three dithienosilicon-bridged carbazole-based (DTSiC) ladder-type (A–DD′D–A) NF-SMAs for AM1.5G/indoor OPVs. First, we synthesize DTSiC-4F and DTSiC-2M, which are composed of a fused DTSiC-based central core with difluorinated 1,1-dicyanomethylene-3-indanone (2F-IC) and methylated IC (M-IC) end groups, respectively. Then, alkoxy chains are introduced in the fused carbazole backbone of DTSiC-4F to form DTSiCODe-4F. From solution to film absorption, DTSiC-4F exhibits a bathochromic shift with strong π–π interactions, which improves the short-circuit current density (J sc) and the fill factor (FF). On the other hand, DTSiC-2M and DTSiCODe-4F display up-shifting lowest unoccupied molecular orbital (LUMO) energy levels, which enhances the open-circuit voltage (V oc). As a result, under both AM1.5G/indoor conditions, the devices based on PM7:DTSiC-4F, PM7:DTSiC-2M, and PM7:DTSiCOCe-4F show power conversion efficiencies (PCEs) of 13.13/21.80%, 8.62/20.02, and 9.41/20.56%, respectively. Furthermore, the addition of a third component to the active layer of binary devices is also a simple and efficient strategy to achieve higher photovoltaic efficiencies. Therefore, the conjugated polymer donor PTO2 is introduced into the PM7:DTSiC-4F active layer because of the hypsochromically shifted complementary absorption, deep highest occupied molecular orbital (HOMO) energy level, good miscibility with PM7 and DTSiC-4F, and optimal film morphology. The resulting ternary OSC device based on PTO2:PM7:DTSiC-4F can improve exciton generation, phase separation, charge transport, and charge extraction. As a consequence, the PTO2:PM7:DTSiC-4F-based ternary device achieves an outstanding PCE of 13.33/25.70% under AM1.5G/indoor conditions. As far as we know, the obtained PCE results under indoor conditions are one of the best binary/ternary-based systems processed from eco-friendly solvents.

Combinatorial screening of wide band-gap organic solar cell materials with open-circuit voltage between 1.1 and 1.4 V

“…18 Other works also achieve high efficiencies with different materials and strategies, therefore showing the potential of OPV for indoor light harvesting. 19–25 For this application, solar cells with high E bg are needed since the light source to be harvested is typically a light-emitting diode (LED), emitting between 400 and 700 nm with a variable spectrum depending on the LED bulb. 26,27 Therefore, devices with E bg below 1.8 eV are expected to suffer from unnecessarily high thermalization losses.…”

Synergy Effect of Symmetry-Breaking and End-Group Engineering Enables 16.06% Efficiency for All-Small-Molecule Organic Solar Cells

“…Organic solar cells (OSCs) have been considered as next-generation energy sources thanks to the merits of lightweight, low-cost solution processability, and flexibility, as well as semitransparency. − At present, the performance of polymer donor-based OSCs has surpassed 19%, which is promoted by molecular innovation, device optimization, and morphology regulation. − All-small-molecule organic solar cells (ASM-OSCs) have practical application values by virtue of their inherent structural advantages including well-defined molecular structures and less variations between batches in comparison with polymer solar cells (PSCs). − However, ASM-OSCs still face challenges in achieving competitive power conversion efficiencies (PCEs). This gap can be imputed to the fact that the morphology control of small molecules is tricky due to stronger crystallization of most small molecules compared to their polymer counterparts. − Nevertheless, multiple variations can be triggered in molecular aggregation, orientation, intermolecular interaction, and blend film morphology by subtle modification of structures. − Therefore, understanding the relationship between the molecular structure and performance of the device by developing novel photovoltaic materials is necessary to improve the PCEs of ASM-OSCs.…”