Abstract
The development of n-type porphyrin acceptors is challenging in organic solar cells. In this work, we synthesized a novel n-type porphyrin acceptor, PZn-TNI, via the introduction of the electron withdrawing naphthalene imide (NI) moiety at the meso position of zinc porphyrin (PZn). PZn-TNI has excellent thermal stability and unique bimodal absorption with a strong Soret band (300–600 nm) and weak Q-band (600–800 nm). The weak long-wavelength absorption of PZn-TNI was completely covered by combining the low bandgap polymer donor, PTB7-Th, which realized the well-balanced panchromatic photon-to-current conversion in the range of 300–800 nm. Notably, the one-step reaction of the NI moiety from a commercially available source leads to the cheap and simple n-type porphyrin synthesis. The substitution of four NIs in PZn ring induced sufficient n-type characteristics with proper HOMO and LUMO energy levels for efficient charge transport with PTB7-Th. Fullerene-free organic solar cells based-on PTB7-Th:PZn-TNI were investigated and showed a promising PCE of 5.07% without any additive treatment. To the best of our knowledge, this is the highest PCE in the porphyrin-based acceptors without utilization of the perylene diimide accepting unit.
Highlights
Organic solar cells (OSCs) have been studied as a portable and low-cost power generator due to their unique advantages: light-weight, use of earth-abundant organic materials, solution-processability and flexibility
The porphyrin ring 1 was synthesized from pyrrole and 3-(trimethylsilyl)propiolaldehyde in the presence of BF3·Et2O followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4benzoquinone (DDQ)
The deprotection of TMS group by tetra-n-butylammonium fluoride (TBAF) was performed immediately before synthesizing the final acceptor, PZn-TNI. 4-Bromo-1,8-naphthalic anhydride purchased from Sigma-Aldrich was alkylated with 2-hexyldexylamine to give a compound 4
Summary
Organic solar cells (OSCs) have been studied as a portable and low-cost power generator due to their unique advantages: light-weight, use of earth-abundant organic materials, solution-processability and flexibility. The final porphyrin acceptor, PZn-TNI, was achieved via Sonogashira coupling with PZn compound 3 and excess of NI compound 4, which was identified by 1H-NMR and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) (Figures S1–S4). The film of PZn-TNI showed broadened n-Type Porphyrin Acceptors and red-shifted Q-band absorption spectra compared to that in solution, indicating the enhanced intermolecular π-π stacking in the film state.
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