A Trialkylsilylthienyl Chain-Substituted Small-Molecule Acceptor with Higher LUMO Level and Reduced Band Gap for Over 16% Efficiency Fullerene-Free Ternary Solar Cells

Abstract

The ternary approach using a smaller band gap acceptor as the near-infrared (NIR) absorber to increase the short-circuit current density (J sc) usually decreases the open-circuit voltage (V oc). In this contribution, we report a small-molecule acceptor, IN-4F, which has a reduced band gap and a higher LUMO level than IT-4F, hence enabling the concurrent increase in the J sc and V oc when using IT-4F as the acceptor guest of the host binary of PM6:IT-4F. IN-4F was judiciously designed by fusing benzodithiophene (BDT) and thieno­[2′,3′:4,5]­thieno to make a larger π-system so as to upshift the LUMO level and reduce the optical band gap and, meanwhile, by substituting the BDT-4,8 positions with trialkylsilylthiophene chains to downshift the HOMO level to match the deep HOMO of PM6. Again, the structural similarity between IN-4F and IT-4F makes the nanoscaled homogeneous fine film morphology and the π–π stacking patterns both well kept; hence, the fill factor (FF) is well maintained. The IN-4F-based binary solar cell shows 13.1% efficiency, and its ternary solar cell blended with IT-4F supplies 14.9% efficiency. Again, the use of IN-4F as the guest acceptor of the PM6:Y6 system enables the increase in V oc due to its higher LUMO level, the increase in J sc because of the increase in charge mobilities, and the maintenance of FF, affording 16.3% efficiency. This work demonstrates that the π-system extending and the trialkylsilylthiophene chain substitution can be an effective strategy to synthesize a nonfullerene acceptor guest to realize a ternary material system, which enables to increase V oc from its entanglement with J sc (an issue of the current material approach).

Molecular Engineering and Morphology Control of Polythiophene:Nonfullerene Acceptor Blends for High‐Performance Solar Cells

“…Organic photovoltaic (OPV) technology has the potential of enormous economic impact due to its unique features such as flexibility, light weight, and potential short energy payback time. [1][2][3][4][5][6][7][8][9][10] With the development of novel nonfullerene acceptors, the power conversion efficiencies (PCEs) of OPVs have been recently boosted to 16-18%, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] which has surpassed the efficiency threshold for commercial applications. With the great progress in device efficiencies, another important issue, cost, should be taken into account for advancing OPV commercialization.…”

Boosting Performance of Non‐Fullerene Organic Solar Cells by 2D g‐C3N4 Doped PEDOT:PSS

“…For further improving the PCE of Y6‐based OSCs, [ 4–7 ] many efforts have been made, such as chemical modification of the Y6, [ 8–11 ] morphological optimization of the active layer, [ 12 ] and introduction of a third component. [ 13–19 ] Besides, interfacial engineering is also a useful strategy to boost the device performance. [ 20–24 ] Noted that most of OSCs based on PM6:Y6 system with high performances adopt poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as hole transport layer (HTL) due to its good film‐forming property, high transparency in the visible region, and solution processability.…”

As‐Cast Ternary Organic Solar Cells Based on an Asymmetric Side‐Chains Featured Acceptor with Reduced Voltage Loss and 14.0% Efficiency

“…Solution‐processed organic solar cells (OSCs) based on the nonfullerene acceptors (NFAs) have drawn extensive attentions due to their diversity of chemical structures, easily tuned energy levels, as well as absorption ranges . Over the past few years, tremendous progress has been made in power conversion efficiencies (PCEs) to reach over 16% for single junction cells and 17.3% for tandem solar cells, which could be ascribed to the rapid development of polymer donors and novel NFAs . More importantly, it has been demonstrated that efficient charge generation and dissociation processes could be realized with small energy offset between the donors and NFAs, which is quite different from those of the fullerene system .…”