Haptacyclic Carbazole-Based Ladder-Type Nonfullerene Acceptor with Side-Chain Optimization for Efficient Organic Photovoltaics

Abstract

In this research, a haptacyclic carbazole-based dithienocyclopentacarbazole (DTCC) ladder-type structure was formylated to couple with two 1,1-dicyanomethylene-3-indanone (IC) moieties, forming a new nonfullerene acceptor DTCCIC-C17 using a bulky branched 1-octylnonayl side chain at the nitrogen of the embedded carbazole and four 4-octylphenyl groups at the sp-carbon bridges. The rigid and coplanar main-chain backbone of the DTCC core provides a broad light-absorbing window and a higher-lying LUMO energy level, whereas the bulky flanked side chains reduce intermolecular interactions, making DTCCIC-C17 amorphous with excellent solution processability. The DTCCIC-C17 as an acceptor is combined with a medium band gap polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] (PBDB-T) as the donor in the active layer to obtain suitable highest occupied molecular orbital/lowest unoccupied molecular orbital energy alignments and complimentary absorption. The devices with an inverted configuration (ITO/ZnO/active layer/MoO/Ag) without using an aqueous poly(3,4-ethylenedioxythiophene) polystyrene sulfonate layer were fabricated for better device stability. When the diiodooctane-treated PBDB-T:DTCCIC-C17 active layer was thermally annealed at 50 °C for 10 min, the device achieved the highest efficiency of 9.48% with a high V of 0.98 V, a J of 14.27 mA cm, and an FF of 0.68.

Improvement of Photovoltaic Performance of Polymer Solar Cells by Rational Molecular Optimization of Organic Molecule Acceptors

“…[16][17][18][19][20][21] Second, suitable side chains are attached on the A-D-A backbone to tune their selfaggregation and miscibility with conjugated polymer donors. On the basis of this type of structure, numerous attempts and improvements have been carried out on the structural modification of the central donor unit and the acceptor end groups as well as their side chains.…”

Small-Molecule Electron Acceptors for Efficient Non-fullerene Organic Solar Cells

“…Two acceptors DTCC-IC and DTCCIC-C17 based on dithienocyclopentacarbazole (DTCC) with different side chains were reported. Due to strong electron-donating properties and coplanar conjugated skeleton, both of them possessed strong absorption and good performance with PCE of 6.0% for DTCC-IC and 9.48% for DTCCIC-C17 (Cao et al, 2017 ; Hsiao et al, 2017 ). Two narrow bandgap acceptors ITTIC (1.46 eV) and ITVffIC (1.35 eV) were synthesized by incorporating thiophene units and double-bond as spacers, respectively.…”

Chlorinated Carbon‐Bridged and Silicon‐Bridged Carbazole‐Based Nonfullerene Acceptors Manifest Synergistic Enhancement in Ternary Organic Solar Cell with Efficiency over 15%

“…In our previous articles, we have reported various fused‐ring structures, [ 3–4,28–32 ] which are valuable in constructing NFAs with decent performance. [ 52–55 ] Recently, we addressed a heptacyclic carbazole‐based NFA named DTC‐4F or DTC(4Ph)‐4FIC, which could afford a decent PCE of 13.37%. [ 53 ] Therefore, the development of dithienocyclopentacarbazole (DTCC) as the electron‐sufficient core for further molecular design is regarded as a promising approach to promote photovoltaic performance.…”