Mingliang Sun

A universal halogen-free solvent system for highly efficient polymer solar cells

Power conversion efficiencies (PCEs) of state-of-the-art polymer solar cells (PSCs) have been promoted to over 9%. However, halogenated solvents like chlorobenzene (CB), o-dichlorobenzene (DCB), 1,8-diiodooctane (DIO) or their mixtures are still predominately used in the fabrication of these high performance PSCs. With the rapid progress in PCEs, removing the halogenated solvents from the fabrication processes of PSCs becomes an urgent task for the practical utilization of PSC technology. In this study, a halogen-free solvent system consisting of o-xylene (XY) and N-methylpyrrolidone (NMP) was successfully applied in the fabrication of the PSCs based on a variety of highly efficient polymers including PBDT-TS1 and other eight types of photovoltaic polymers. Notably, utilizing an XY–2% NMP mixture as a processing solvent, the PBDT-TS1/PC71BM-based PSC realized a PCE of 9.47%, which has been the highest value in halogen-free solvent processed PSCs until now. The photovoltaic properties and nanoscale morphology clearly indicated that the halogen-free solvent system featuring the XY–NMP mixture can replace the role of the widely utilized halogenated solvents in fabricating environmentally friendly PSCs with high efficiency.

Pyrite FeS2 microspheres wrapped by reduced graphene oxide as high-performance lithium-ion battery anodes

A composite of pyrite FeS2 microspheres wrapped by reduced graphene oxide (FeS2/rGO) has been synthesized by a facile one-step solvothermal method and applied as an anode in lithium ion batteries (LIBs). Impedance measurements and transmission electron microscopy show that incorporation of rGO significantly decreases the charge transfer resistance and improves the structural stability of the composite. As an anode material for LIBs, the composite exhibits a high capacity of 970 mA h g−1 at a current density of 890 mA g−1 after 300 cycles. Additionally, this composite anode shows impressive performance especially at high current densities. The LIB shows a capacity of 380 mA h g−1 even at a high current density of 8900 mA g−1 (10C) over 2000 cycles, demonstrating its potential for applications in LIBs with long cycling life and high power density.

Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability

Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function.

High-Performance Photovoltaic Polymers Employing Symmetry-Breaking Building Blocks.

Two 1D-2D asymmetric benzodithiophenes (BDTs) as donor building blocks are designed and synthesized, combining the advantages of both 1D and 2D symmetric BDTs. The photovoltaic properties of the asymmetric BDT-based polymers are improved greatly in comparison with corresponding symmetric BDT-based polymers. This work provides a new approach to design prospective organic optoelectronic materials employing the symmetry-breaking strategy.

Facile fabrication and electrochemical properties of high-quality reduced graphene oxide/cobalt sulfide composite as anode material for lithium-ion batteries

A reduced graphene oxide (rGO)/cobalt sulfide composite is synthesized with a simple and efficient ultrasound-assisted wet chemical method. The morphology and microstructure of the composite are examined with field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results confirm that cobalt sulfide nanoparticles are homogeneously and tightly attached on the surfaces of rGO. As an anode material for lithium-ion batteries, this composite delivers a high reversible capacity of 994 mA h g−1 after 150 cycles at a current density of 200 mA g−1. A synergistic effect combining the merits of rGO and cobalt sulfide nanoparticles endows the composite with superior electrochemical performances over those of pure cobalt sulfide.

Simple planar perovskite solar cells with a dopant-free benzodithiophene conjugated polymer as hole transporting material

Dopant-free poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b] thiophene)-2,6-diyl] (PBDTTT-C) polymer is used as hole transporting material (HTM) in electron transporting material (ETM) free planar perovskite solar cells (PSCs). The devices with a PBDTTT-C HTM show higher power conversion efficiency (PCE = 9.95%) than the devices with a P3HT HTM (PCE = 6.17%) with enhanced short circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF) in a simple device configuration (ITO/CH3NH3PbI3/PBDTTT-C/MoO3/Ag), due to the suitable energy level, better carrier mobility and lower interfacial charge recombination.

Enhanced efficiency of polymer photovoltaic cells via the incorporation of a water-soluble naphthalene diimide derivative as a cathode interlayer

In this contribution, a novel cathode interlayer material (NDIO) based on naphthalene diimide was successfully prepared by a facile two-step reaction from commercially available compounds. NDIO exhibited excellent water solubility, high transparency in the visible light region, and well-matched molecular energy levels. By incorporating this novel water processed cathode interlayer, a high power conversion efficiency of 9.51% was recorded in PBDT-TS1/PC71BM-based polymer photovoltaic cells (PPCs), and the value is nearly 2-fold the device efficiency of PPCs without the cathode interlayer. More importantly, the insertion of the NDIO interlayer promotes the device efficiency of polymer/polymer photovoltaic cells based on PBDTTT-EFT/N2200 from 3.23% up to 5.77%. The successful applications in both polymer/PCBM and polymer/polymer blend-based inverted PPCs make NDIO a promising cathode interlayer for realizing aqueous processed polymer photovoltaic cells with high performance.

Hyperconjugated side chained benzodithiophene and 4,7-di-2-thienyl-2,1,3- benzothiadiazole based polymer for solar cells

A novel donor–acceptor (D–A) copolymer (P3TBDTDTBT), including hyperconjugated side chained benzodithiophene as a donor and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) as an acceptor, was designed and synthesized. Due to the introduction of the hyperconjugated side chain, the resultant polymer exhibited good thermal stability with a high decomposition temperature of 437 °C, a low band-gap of 1.67 eV with an absorption onset of 742 nm in the solid film, and a deep highest occupied molecular orbital (HOMO) energy level of −5.26 eV. Finally, the polymer solar cell (PSC) device based on this polymer and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) showed the best power conversion efficiency (PCE) of 3.57% with an open-circuit voltage (Voc) of 0.78 V, a short-circuit current density (Jsc) of 8.83 mA cm−2 and a fill factor (FF) of 53%.

High efficiency solution-processed two-dimensional small molecule organic solar cells obtained via low-temperature thermal annealing

A new two-dimensional (2D) organic small molecule, DCA3T(T-BDT), was designed and synthesized for solution-processed organic solar cells (OSCs). DCA3T(T-BDT) exhibited a deep HOMO energy level (−5.37 eV) and good thermal stability. The morphologies of the DCA3T(T-BDT):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends were investigated by atomic force microscopy and the crystallinity was explored by X-ray diffraction (XRD) and 2D grazing incidence wide-angle X-ray scattering (GIWAXS), respectively. The morphologies of the blends were strongly influenced by the blend ratio of DCA3T(T-BDT):PC61BM and annealing temperature. The effect of thermal annealing on the photovoltaic performance of DCA3T(T-BDT)-based small molecule organic solar cells (SMOSCs) was studied in detail. When DCA3T(T-BDT) was used as a donor with PC61BM as an acceptor, high efficiency SMOSCs with a power conversion efficiency of 7.93%, a high Voc of 0.95 V, Jsc of 11.86 mA cm−2 and FF of 0.70 were obtained by a thermal annealing process at only 60 °C, which offers obvious advantages for large scale production compared with solvent additive or interfacial modification treatment.

Solution-processed, indacenodithiophene-based, small-molecule organic field-effect transistors and solar cells

Two indacenodithiophene-based molecules with different side chains, BTIDT-C6 and BTIDT-OC12, have been designed and synthesized for solution-processed, small-molecule organic solar cells (OSCs) donor materials. By optimizing the side chains, the hole mobility of the materials is modulated, which has been proven by the organic field-effect transistor (OFET) performances. Solar cells based on BTIDT-C6 show a power conversion efficiency (PCE) of 4.83%. To the best of our knowledge, this is the first report about indacenodithiophene-based, solution-processed, small-molecule OFETs, and it is also one of the highest PCE reports for the indacenodithiophene-based, solution-processed, small-molecule OSCs. This report makes indacenodithiophene-based small molecules the third type of high-efficiency (5% PCE), solution-processed, small-molecule OSCs donor materials, in addition to benzodithiophene (BDT) and dithienosilole (DTS).