sheng Li

Deep Absorbing Porphyrin Small Molecule for High-Performance Organic Solar Cells with Very Low Energy Losses

We designed and synthesized the DPPEZnP-TEH molecule, with a porphyrin ring linked to two diketopyrrolopyrrole units by ethynylene bridges. The resulting material exhibits a very low energy band gap of 1.37 eV and a broad light absorption to 907 nm. An open-circuit voltage of 0.78 V was obtained in bulk heterojunction (BHJ) organic solar cells, showing a low energy loss of only 0.59 eV, which is the first report that small molecule solar cells show energy losses <0.6 eV. The optimized solar cells show remarkable external quantum efficiency, short circuit current, and power conversion efficiency up to 65%, 16.76 mA/cm(2), and 8.08%, respectively, which are the best values for BHJ solar cells with very low energy losses. Additionally, the morphology of DPPEZnP-TEH neat and blend films with PC61BM was studied thoroughly by grazing incidence X-ray diffraction, resonant soft X-ray scattering, and transmission electron microscopy under different fabrication conditions.

Solution-processed bulk heterojunction solar cells based on a porphyrin small molecule with 7% power conversion efficiency

A porphyrin small molecule with less bulky substituents at the porphyrin periphery has been synthesized as a donor material, which exhibits a power conversion efficiency of up to 7.23% under AM 1.5 G irradiation (100 mW cm−2) for the solution-processed bulk heterojunction solar cells with PC61BM as the acceptor material.

Enhanced performance of solution-processed solar cells based on porphyrin small molecules with a diketopyrrolopyrrole acceptor unit and a pyridine additive

A conjugated donor–acceptor porphyrin small molecule was designed and synthesized with diketopyrrolopyrrole as the acceptor unit. The new porphyrin-based small molecule exhibits broad and intense absorption in the visible and near IR regions, and the hole mobility and the power conversion efficiency of the bulk heterojunction devices based on the porphyrin : [6,6]-phenyl-C-61-butyric acid methyl ester (1 : 1, w/w) are increased up to 4.6 × 10−5 cm2 V−1 s−1 and 3.71%, respectively, which are further enhanced to 1.6 × 10−4 cm2 V−1 s−1 and 4.78%, respectively, upon the introduction of 3.0 vol% of pyridine additive. Further studies show that the performance of the solar cells based on other zinc porphyrins could also be improved by the pyridine additive.

Solution processed small molecule bulk heterojunction organic photovoltaics based on a conjugated donor–acceptor porphyrin

Due to the π-conjugation of the whole molecule along with the push–pull property of a newly designed conjugated donor–acceptor porphyrin, the solution processed solar cells using the blend of the porphyrin small molecule with PC71BM exhibit a promising performance with a power conversion efficiency of up to 4.02%.

High-Efficiency Small Molecule-Based Bulk-Heterojunction Solar Cells Enhanced by Additive Annealing

Solvent additive processing is important in optimizing an active layers morphology and thus improving the performance of organic solar cells (OSCs). In this study, we find that how 1,8-diiodooctane (DIO) additive is removed plays a critical role in determining the film morphology of the bulk heterojunction OSCs in inverted structure based on a porphyrin small molecule. Different from the cases reported for polymer-based OSCs in conventional structures, the inverted OSCs upon the quick removal of the additive either by quick vacuuming or methanol washing exhibit poorer performance. In contrast, the devices after keeping the active layers in ambient pressure with additive dwelling for about 1 h (namely, additive annealing) show an enhanced power conversion efficiency up to 7.78% with a large short circuit current of 19.25 mA/cm(2), which are among the best in small molecule-based solar cells. The detailed morphology analyses using UV-vis absorption spectroscopy, grazing incidence X-ray diffraction, resonant soft X-ray scattering, and atomic force microscopy demonstrate that the active layer shows smaller-sized phase separation but improved structure order upon additive annealing. On the contrary, the quick removal of the additive either by quick vacuuming or methanol washing keeps the active layers in an earlier stage of large scaled phase separation.

Highly responsive organic near-infrared photodetectors based on a porphyrin small molecule

Solution processed organic near-infrared (NIR) photodetectors (PDs) based on a porphyrin small molecule as a donor material and (6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) as an acceptor material are reported. Operating at room temperature, these PDs show a low dark current density of 3.44 nA cm−2, a broad spectral response from 380 to 960 nm with high external quantum efficiencies around 20% in the NIR region at a bias of 0 V. Detectivities over 1012 cm H1/2 W−1 in the whole range from 380 to 930 nm are achieved, which rank as one of the best performances among previously reported NIR PDs.

Water redissoluble chiral porphyrin–carbon nanotube composites

The redissoluble functional compound/carbon nanotube (CNT) composites are important for post processing because CNT dispersions usually easy aggregate and therefore make additional processing very difficult. Due to the outstanding electronic, photophysical and photochemical properties of porphyrin and CNT composites, the chiral nanocomposites of chiral porphyrins and single-walled carbon nanotubes (SWNTs) are quite promising for applications in chiral catalysis and bio-sensing. The porphyrins used for the solubilization of CNTs are usually tetra-phenyl porphyrin (TPP) analogues. However, TPP analogues do not favor the formation of π–π interactions because the aryl groups prevent the porphyrin moiety from approaching the CNT surface due to the perpendicular conformation of the porphyrin moiety and its aryl group substituents. In this paper, non-TPP type porphyrins with chiral and hydrophilic substituents, that make the porphyrins soluble in water, were synthesized. SWNTs were effectively dissolved into water by the non-TPP type chiral porphyrins, and the dissolved chiral porphyrin/SWNTs composites could be easily redissolved. Both the dissolved and redissolved SWNT solutions are very stable and did not form apparent aggregates even after being kept for six months. Spectroscopic studies show that the binding properties of the chiral porphyrins to SWNTs are different in basic and neutral solution, which should contribute to the development and understanding in the study of sensors, biosensors, and catalysts made from chiral molecule/CNT composites.

π-conjugated donor-acceptor porphyrin copolymers for organic photovoltaics

Abstract. Conjugated donor–acceptor (D-A) molecular structures play a very important role in the significant progress of organic photovotaics. However, the reports on conjugated D-A porphyrin polymers for organic solar cells are very limited. In this work, five conjugated D-A porphyrin copolymers PEZPEBTA(C12), PEZPEBT, PEZPEBTff, PEZPETPD(O), and PEZPETDPPT(O) were synthesized by Sonagashira coupling of a porphyrin donor unit with five typical acceptor units 2-dodecyl-2H-benzotriazole, benzo[1,2,5]thiadiazole, 5,6-difluoro-benzo[1,2,5]thiadiazole, 5-octyl-thieno[3,4-c]pyrrole-4,6-dione, and 3,6-bis-(thiophen-2-yl)-2,5-dioctyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione linked by ethynylene linkages, respectively. They possess excellent thermal stability with a decomposition temperature of around 400°C. All absorption spectra of the copolymers were significantly red shifted with enhanced Q bands at the near-infrared region both in solutions and in films due to the simultaneous introduction of ethynylene linkages and acceptor units, which make the polymer main chains coplanar and π-conjugated and enhance the intramolecular charge transfer. PEZPEBT and PEZPEBTff are electrochemically active in both the oxidation and reduction regions, while PEZPEBTA(C12), PEZPETPD(O), and PEZPETDPPT(O) show only oxidation peaks. Power conversion efficiencies of 0.12%, 0.41%, 0.26%, 0.19%, and 0.41% were achieved for the polymer solar cells based on PEZPEBTA(C12), PEZPEBT, PEZPEBTff, PEZPETPD(O), and PEZPETDPPT(O), respectively, under AM 1.5, 100  mW/cm2 with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) (1:2, w/w) as the active layer in the presence of 3% pyridine.