Energy-level modulation of coumarin-based molecular donors for efficient all small molecule fullerene-free organic solar cells

Abstract

Despite their minimal HOMO energy level offset promising power conversion efficiencies up to 13.54% have been recorded for ternary organic solar cells using coumarin-based molecular donors and fullerene-free acceptors.

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%

“…The cascade energy levels formed between the three molecules are more conducive for efficient charge transport in the active layer. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of C2, DBTBT-IC, and AQx-3 in film states were estimated by cyclic voltammetry under similar conditions using Fc/Fc + as the internal standard (Figure S2, Supporting Information). The HOMO/LUMO energies of C2, DBTBT-IC, and AQx-3 are presented in Figure c.…”

“…19 Similarly, a medium-band-gap dibenzothieno [3,2-b][1]benzothiophenebased FFSMA, DBTBT-IC when used as the secondary acceptor in a polymer solar cell using a polymer donor PDTNIT with a similar backbone and PC 71 BM acceptor gave a PCE of 15.9%. 57 On the basis of the above outcomes, in this work we used these two FFSMAs and a wide-band-gap coumarin-based molecular donor C2 58 with complementary absorption in order to cover a broad spectral range and fabricated all-small-molecule binary and ternary OSCs. The allsmall-molecule ternary device C2:DBTBT-IC:AQx-3 (1:0.2:1.0) achieved an overall PCE of 14.49%, which is significantly higher than both binary devices (10.02% for C2:DBTBT-IC and 10.86% for C2:AQx-3).…”

Recent Progress in the Design of Fused-Ring Non-Fullerene Acceptors─Relations between Molecular Structure and Optical, Electronic, and Photovoltaic Properties

“…Since it consists of only five fused rings, it permits the investigation of, for example, various end groups, without imposing too dominant effects itself. IDIC and its halogenated derivatives are often used for the development of new donor polymers , or small molecule donors. ,− …”

Strongly Reduced Non-Radiative Voltage Losses in Organic Solar Cells Prepared with Sequential Film Deposition

“…In the majority of fullerene acceptor-based OSCs, a high charge generation efficiency is often achieved at the expense of experiencing a large photovoltage loss (Δ V oc ), due to the large energetic offsets between the frontier molecular levels of donors and fullerene acceptors (Δ E offset ). , With the development of non-fullerene acceptors (NFAs) with highly tunable energetics, the Δ V oc can be reduced via the decrease in Δ E offset . In some recently reported low-offset BHJ systems associated with low Δ V oc values, efficient charge generation has been observed, which could be explained by the long-lived charge-transfer (CT) state, strong electronic coupling, or electrostatic interactions . To realize these targeted properties in NFA-OSCs, the nanoscale phase morphology in the BHJ films needs to be carefully optimized to achieve suitable phase separation and molecular packing. , However, due to the coexistence of the D and A components in the BHJ solutions, obtaining a well-controlled phase morphology in solid state BHJ films thermodynamically tends to be difficult, which can be affected by many factors. − …”

“…4,5 With the development of nonfullerene acceptors (NFAs) with highly tunable energetics, the ΔV oc can be reduced via the decrease in ΔE offset . 6 In some recently reported low-offset BHJ systems associated with low ΔV oc values, 7 efficient charge generation has been observed, which could be explained by the long-lived charge-transfer (CT) state, 8 strong electronic coupling, 9 or electrostatic interactions. 10 To realize these targeted properties in NFA-OSCs, the nanoscale phase morphology in the BHJ films needs to be carefully optimized to achieve suitable phase separation and molecular packing.…”