Xiaobin Peng

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.

11% Efficient Ternary Organic Solar Cells with High Composition Tolerance via Integrated Near-IR Sensitization and Interface Engineering.

Highly efficient electron extraction is achieved by using a photoconductive cathode interlayer in inverted ternary organic solar cells (OSCs) where a near-IR absorbing porphyrin molecule is used as the sensitizer. The OSCs show improved device performance when the ratio of the two donors varies in a large region and a maximum power conversion efficiency up to 11.03% is demonstrated.

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.

High-Performance Polymer Tandem Solar Cells Employing a New n-Type Conjugated Polymer as an Interconnecting Layer.

UNLABELLED A new n-type polymer, PF3N-2TNDI, with high electron mobility, is developed as efficient cathode interfacial material and interconnecting layer (ICL) for constructing high-performance tandem organic solar cells. Tandem cells employing the ICL with structure of PF3N-2TNDI/Ag/ PEDOT PSS achieve a high power conversion efficiency (PCE) of 11.35%. Moreover, flexible tandem cells with PCE over 10% are also demonstrated.

Multi-Length-Scale Morphologies Driven by Mixed Additives in Porphyrin-Based Organic Photovoltaics.

A new category of deep-absorbing small molecules is developed. Optimized devices driven by mixed additives show a remarkable short-circuit current of ≈20 mA cm(-2) and a highest power conversion efficiency of 9.06%. A multi-length-scale morphology is formed, which is fully characterized by resonant soft X-ray scattering, high-angle annular dark film image transmission electron microscopy, etc.

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%.

Simultaneous Discrimination of Handedness and Diameter of Single-Walled Carbon Nanotubes (SWNTs) with Chiral Diporphyrin Nanotweezers Leading to Enrichment of a Single Enantiomer of (6,5)-SWNTs

Separation of single-walled carbon nanotubes (SWNTs) according to their handedness has been attracting growing interest. Our methodology to separate the enantiomers of SWNTs is based on molecular recognition with chiral diporphyrin nanotweezers. Herein, we report novel nanotweezers 1 consisting of two chiral porphyrins and phenanthrene in between. These nanotweezers 1 are rationally designed to discriminate diameter and handedness simultaneously by taking into account the relationship between the (n, m) selectivity and the structures of previously reported chiral nanotweezers. Owing to the relatively narrow cleft made by two porphyrins, the nanotweezers 1 showed high selectivity toward (6,5)-SWNTs possessing the smallest diameter among the major components of CoMoCAT-SWNTs. In addition, the chiral diporphyrin 1 discriminated the left- and right-handed structures of (6,5)-SWNTs, providing high enantiomeric excess (67% ee on the basis of the (6,5)-SWNTs with high optical purity recently reported by Weisman). In conclusion, only the single stereoisomer of (6,5)-SWNTs was highly enriched through the extraction of CoMoCAT-SWNTs with phenanthrene-bridged chiral diporphyrin nanotweezers 1.

Excitation energy migration processes in cyclic porphyrin arrays probed by single molecule spectroscopy.

By using single molecule fluorescence spectroscopy we have investigated the excitation energy migration processes occurring in a series of cyclic porphyrin arrays bearing a close proximity in overall architectures to the LH2 complexes in purple bacterial photosynthetic systems. We have revealed that the conformational heterogeneity induced by the structural flexibility in large cyclic porphyrin arrays, which provides the nonradiative deactivation channels as an energy sink or trap, reduces significantly the energy migration efficiency. Our study provides detailed information on the energy migration efficiency of the artificial light-harvesting arrays at the single molecule level, which will be a guideline for future applications in single molecular photonic devices in the solid state.

A complementary absorption small molecule for efficient ternary organic solar cells

Ternary solar cells are emerging as an attractive strategy to enhance the power conversion efficiencies (PCEs) of binary ones while maintaining the simple processing of single junction devices rather than that of the more complex tandem cells. However, only a few successful ternary blend solar cells have been reported with improved device performance. In this study, a low band gap small molecule DPPEZnP-O, which shows complementary absorption to PTB7, is introduced into PTB7 : PC71BM (PTB7: poly-thieno[3,4-b]thiophene/benzodithiophene; PC71BM: (6,6)-phenyl-C71-butyric acid methyl ester) to fabricate ternary solar cells. A PCE of 8.39% is achieved for the bulk heterojunction (BHJ) ternary solar cells with 20% DPPEZnP-O, which is a 12% enhancement in PCE compared with the binary OSCs based on PTB7 : PC71BM. DPPEZnP-O in PTB7 : PC71BM not only broadens light absorption to the near infrared region from 750 to 900 nm to harvest more photons but also plays a bridging role between PTB7 and PC71BM to provide more charge transfer routes at D/A interfaces. Unlike in many cases, 20% DPPEZnP-O in PTB7 : PC71BM does not form recombination centers to suppress the charge transport process, which also plays a role in the enhanced OSC performance.