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

Abstract

The small-molecule-based donor/acceptor blend is an important component in bulk-heterojunction organic solar cells (OSCs). Although a variety of small-molecule donors have been developed in recent years, only a few of them have reached efficiencies over 15% using fullerene-free acceptors in OSCs. Therefore, it is important to develop high-performing molecular donor materials with ideal molecular orbital energy levels, complementary absorption to the acceptors, and good charge-transporting character. Herein, the design and development of two wide band gap functional coumarin-based donor materials C1-CN and C2-CN are presented, which are synthesized efficiently using readily accessible starting materials, an important criterion for the realization of cost-effective large area OSCs. The associated effect of excellent optoelectronic and thermal properties and frontier orbital energy levels enabled the application of the synthesized donors in solution-processed fullerene-free OSCs. Ternary OSCs fabricated with C1-CN:DBTBT-IC:Y6 displayed efficiencies up to 15.28%, one of the highest values reported for all-small-molecule OSCs with a low energy loss of 0.43 eV.

Achieving High‐Efficiency in Binary Organic Solar Cells by the Structural Fine‐Tuning of Coumarin‐Based Donor

“…In these donor and acceptor molecules, the short‐wavelength absorption peaks between 300 and 400 nm are associated with localized π–π* transition. In comparison to C1–CN, [ 31 ] the extension of π‐conjugation in C3–CN red‐shifted the absorption (Δ λ max = 14 nm) and lowered the bandgap (Δ E g = 0.14 eV) in thin films. The molecules showed emission maximum at 591 and 580 nm, respectively, for C3 and C3–CN.…”

“…[14,[19][20][21][22][23][24][25][26][27][28] Recently, we have introduced carbonyl and dicyanomethylenesubstituted coumarin derivatives C1 and C1-CN in binary BHJOSCs generating PCEs between 8% and 10.5% using several FFAs (Figure 1). [29][30][31] The performance was ascribed to the strong and complementary absorption, more exciton generation due to the increased surface area of the interfaces in the blend, and efficient charge transport due to matching energy levels. Inspired by the success of implementing coumarin as a donor material in attaining the high PCE, herein, we developed two new coumarin-based small molecule donors, namely C3 and C3-CN, by the introduction of double bonds in the π-conjugated chain.…”

All-small-molecule efficient ternary organic solar cells employing a coumarin donor and two fullerene-free acceptors

“…[26][27][28][29][30][31] A lot of research has been devoted to developing all-small-molecule OSCs, and PCEs in the range of 15-17% have been attained for binary and ternary devices. [32][33][34][35][36][37][38] Herein, we have used two FFAs, i.e., one narrow bandgap and the other medium bandgap, denoted as F13 39 and IDT-IC, 40 respectively, and a wide bandgap small molecule C1-CN donor 41 for the construction of ternary ASM-OSCs. The chemical structures of these molecules are shown in Fig.…”

“…Herein, we have used two FFAs, i.e. , one narrow bandgap and the other medium bandgap, denoted as F13 39 and IDT-IC, 40 respectively, and a wide bandgap small molecule C1-CN donor 41 for the construction of ternary ASM-OSCs. The chemical structures of these molecules are shown in Fig.…”

Diketopyrrolopyrrole-Coumarin Conjugates for Efficient Binary Organic Solar Cells

“…Coumarin, a natural and synthetic heterocyclic compound, and their derivatives have been widely used for a range of applications such as dye-sensitized solar cells, − OSCs, − organic light-emitting diodes, and as a fluorescence emitter because of their high stability, good structural flexibility, and intrinsic high photoluminescence (PL) quantum yields . A weakly fluorescent coumarin could exhibit excellent fluorescence on proper substitution on the core with various chromophores.…”