Fullerene-Free All-Small-Molecule Ternary Organic Solar Cells with Two Compatible Fullerene-Free Acceptors and a Coumarin Donor Enabling a Power Conversion Efficiency of 14.5%

Abstract

Organic solar cells (OSCs) based on a ternary single bulkheterojunction using either donor:donor:acceptor or donor:acceptor:acceptor with complementary absorption profiles and well-matched energy levels can effectively improve the power conversion efficiency (PCE). Herein, we report the fabrication of binary and ternary OSCs using a wide-band-gap donor molecule C2 in combination with two fullerene-free acceptors (FFAs), i.e., a medium-band-gap DBTBT-IC and a low-band-gap AQx-3. After incorporation of DBTBT-IC in the host C2:AQx-3 binary BHJ active layer, the ternary blend C2:DBTBT-IC:AQx (1.0:0.2:1.0) attains a PCE of 14.49%, which outperforms the respective binary devices, i.e., 10.02% for C2:DBTBT-IC and 10.86% for C2:AQx-3. The higher PCE of the ternary OSC may be related to the simultaneous increase in both the photocurrent (J SC ) and the fill factor (FF). The enhancement in the J SC may be associated with the increase in the lightharvesting efficiency of the ternary blend, efficient utilization of the exciton via the energy transfer from DBTBT-IC to AQx-3, and more channels for the charge transfer in the ternary OSC. The higher FF for the ternary devices may be associated with the efficient charge transport and suppression of charge recombination due to appropriate nanoscale phase separation. Thus, the use of a smallmolecule donor and two FFAs with complementary absorptions and band gaps may be a good strategy to fabricate efficient ternary OSCs.

Medium Bandgap Nonfullerene Acceptor for Efficient Ternary Polymer Solar Cells with High Open-Circuit Voltage

“…Additionally, the fill factor (FF) of the PSCs is improved, and the charge carrier transit is improved by an appropriate cascade energy level structure, which also suppresses the recombination processes . In some cases, the third component can act as an additional energy donor by forming an efficient energy transfer channel with the host binary system and improving the efficiency of photogenerated exciton generation. − This occurs when the third component’s PL spectrum overlaps with the host’s (donor or acceptor) absorption spectra.…”

High-Efficiency Ternary Organic Solar Cells Enabled by Synergizing Dicyanomethylene-Functionalized Coumarin Donors and Fullerene-Free Acceptors

“…Sharma and co-workers reported a PCE of 13.1% with a Δ E HOMO of 0.14 eV . Our group recently reported two coumarin-based wide band gap donor molecules (C1 and C2) attaining PCEs of 11.1–14.5% in ternary OSCs with low E loss . − The blend of C2:BThIND-Cl and C2:Y6 acceptors showed PCEs of 9.46% and 9.72%, respectively, despite a small Δ E HOMO of 0.02–0.04 eV resulting from the reduction of the nonradiative loss …”

Correlation of Functional Coumarin Dye Structure with Molecular Packing and Organic Solar Cells Performance

“…Hence, the inclusion of the third component into the binary blend offers a simplistic approach to improve the light harvesting properties as well as stability. [21][22][23][24][25][26][27] Zhu and co-workers recently reported a PCE of 18% using a polymer donor PM6 along with Y6 and AQx-3 as dual-electron acceptors. [28] The "two-in-one" strategy reinforced the film morphology via alloy formation facilitating charge generation and transport.…”

“…Recent literatures revealed that the use of coumarin-based donor molecules [25,27,29] in the photoactive layer can compete with the well-known donor molecules based on benzodithiophene (BDT), diketopyrrolopyrrole (DPP), oligothiophenes, and dithienopyrrole (DTP). [30][31][32][33][34][35] The coumarin derivatives possess well-matched energy levels, light absorption in the high-energy region of the visible spectrum, and suitable miscibility properties with the fullerene-free acceptors, offering PCE up to 15% in ternary OSCs.…”