New Wide Band Gap Donor for Efficient Fullerene-Free All-Small-Molecule Organic Solar Cells

Abstract

A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (E) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of -5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (V = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor-acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.

An Alkylated Indacenodithieno[3,2‐b]thiophene‐Based Nonfullerene Acceptor with High Crystallinity Exhibiting Single Junction Solar Cell Efficiencies Greater than 13% with Low Voltage Losses

“…Among the highest performing NFAs, linear rod-like acceptor-donor-acceptor (A-D-A) structures incorporating fused ladder-type aromatics have attracted much interest. Common donor units include 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene (IDT) [5][6][7][8][9] and 6,12-dihydro-dithienoindeno [10][11][12][13][14][15][16][17][18] In both cases, the fused core facilitates π-electron delocalization and improves the π-π stacking between molecules, hence enhancing the intrinsic charge carrier mobility.In 2015, Zhan and coworkers reported a new NFA, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11--b′]dithiophene (ITIC) (Scheme 1), which is comprised an electron-donating IDTT-based core flanked by two electron-withdrawing units of 1,1-dicyanomethylene-3-indanone (IC), that exhibited a promising PCE of 6.8% at that time. [10] Since then, many strategies have been applied to modify the structure of ITIC in order to adjust the absorption spectra and energy levels to further improve the PCE, for example, by changing the side chains, [17,18] extending the conjugation length, [19][20][21][22] and substituting the end acceptor groups.…”

“…Among the highest performing NFAs, linear rod-like acceptor-donor-acceptor (A-D-A) structures incorporating fused ladder-type aromatics have attracted much interest. Common donor units include 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene (IDT) [5][6][7][8][9] and 6,12-dihydro-dithienoindeno [10][11][12][13][14][15][16][17][18] In both cases, the fused core facilitates π-electron delocalization and improves the π-π stacking between molecules, hence enhancing the intrinsic charge carrier mobility.…”

Rationalizing Small‐Molecule Donor Design toward High‐Performance Organic Solar Cells: Perspective from Molecular Architectures

“…[8,9,[38][39][40] Here, taking the DRTB-T/IT-4F system ( Figure 1b) as representative, we have investigated the frontier molecular orbital levels (Figure 2), blending morphology (Figure S6, Supporting Information), and electronic couplings for ED and CR (Figure 3). However, the interfacial geometries and charge transport properties are more complicated and difficult to control due to the anisotropic backbones for both donors and acceptors.…”

“…[4,5,[10][11][12][13][14][15][16][17][18][19] This significant improvement is attributed to the great efforts in developing new SM donors and device optimizations. [8,9,[38][39][40] To realize solution processing in organic solvents, alkyl side chains are necessary to attach to the It is noteworthy that most of the donors with PCEs over 9% are of A-π -D-π -A structures.…”

“…It is noteworthy that most of the donors with PCEs over 9% are of A-π -D-π -A structures. [8,9,[38][39][40] To realize solution processing in organic solvents, alkyl side chains are necessary to attach to the [8,9,[34][35][36][37] Similarly, for nonfullerene SM OSCs with PCEs over 9%, both the donors and acceptors adopt A-π -D-π -A and/or Aπ -A structures.…”