One-step electrochemical synthesis of nitrogen and sulfur co-doped, high-quality graphene oxide.

High-quality graphene oxide (GO) with high crystallinity and electrical conductivity as well as in situ doped with nitrogen and sulfur is obtained via the electrochemical exfoliation of graphite. Furthermore, iron incorporated GO sheets show promising catalytic activity and stable methanol tolerance durability when used as electrocatalysts for the oxygen reduction reaction.

Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.

Successful implementation of molecular solution processing from a homogeneous and stable precursor would provide an alternative, robust approach to process multinary compounds compared with physical vapor deposition. Targeting deposition of chemically clear, high quality crystalline films requires specific molecular structure design and solvent selection. Hydrazine (N2H4) serves as a unique and powerful medium, particularly to incorporate selected metallic elements and chalcogens into a stable solution as metal chalcogenide complexes (MCC). However, not all the elements and compounds can be easily dissolved. In this manuscript, we demonstrate a paradigm to incorporate previously insoluble transitional-metal elements into molecular solution as metal-atom hydrazine/hydrazine derivative complexes (MHHD), as exemplified by dissolving of the zinc constituent as Zn(NH2NHCOO)2(N2H4)2. Investigation into the evolution of molecular structure reveals the hidden roadmap to significantly enrich the variety of building blocks for soluble molecule design. The new category of molecular structures not only set up a prototype to incorporate other elements of interest but also points the direction for other compatible solvent selection. As demonstrated from the molecular precursor combining Sn-/Cu-MCC and Zn-MHHD, an ultrathin film of copper zinc tin sulfide (CZTS) was deposited. Characterization of a transistor based on the CZTS channel layer shows electronic properties comparable to CuInSe2, confirming the robustness of this molecular solution processing and the prospect of earth abundant CZTS for next generation photovoltaic materials. This paradigm potentially outlines a universal pathway, from individual molecular design using selected chelated ligands and combination of building blocks in a simple and stable solution to fundamentally change the way multinary compounds are processed.

High performance low band gap polymer solar cells with a non-conventional acceptor.

A novel C70 fullerene derivative was designed and synthesized by [4+2] cyclic addition reaction between indene derivative (methyl 1H-indene-3-carboxylate) and C70. The absorption and photoluminescence of H120 and its mixed films with different polymer donor materials were investigated, as well as its electrochemical property and electron mobility. It was found that H120 has 0.05 eV higher LUMO level than that of PC(70)BM. Its electron mobility reached 6.32 × 10(-4) cm(2) V(-1) s(-1), which is slightly lower than 9.55 × 10(-4) cm(2) V(-1) s(-1) of PC(70)BM. The photovoltaic devices based on P3HT, and two high efficiency low band gap polymers, PBDTTT-C and PBDTTDPP as donors, with H120 as an acceptor gave power conversion efficiencies of 4.2%, 6.0% and 6.2%, respectively.

Systematic investigation of benzodithiophene- and diketopyrrolopyrrole-based low-bandgap polymers designed for single junction and tandem polymer solar cells.

The tandem solar cell architecture is an effective way to harvest a broader part of the solar spectrum and make better use of the photonic energy than the single junction cell. Here, we present the design, synthesis, and characterization of a series of new low bandgap polymers specifically for tandem polymer solar cells. These polymers have a backbone based on the benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) units. Alkylthienyl and alkylphenyl moieties were incorporated onto the BDT unit to form BDTT and BDTP units, respectively; a furan moiety was incorporated onto the DPP unit in place of thiophene to form the FDPP unit. Low bandgap polymers (bandgap = 1.4-1.5 eV) were prepared using BDTT, BDTP, FDPP, and DPP units via Stille-coupling polymerization. These structural modifications lead to polymers with different optical, electrochemical, and electronic properties. Single junction solar cells were fabricated, and the polymer:PC(71)BM active layer morphology was optimized by adding 1,8-diiodooctane (DIO) as an additive. In the single-layer photovoltaic device, they showed power conversion efficiencies (PCEs) of 3-6%. When the polymers were applied in tandem solar cells, PCEs over 8% were reached, demonstrating their great potential for high efficiency tandem polymer solar cells.

Fused silver nanowires with metal oxide nanoparticles and organic polymers for highly transparent conductors.

Silver nanowire (AgNW) networks are promising candidates to replace indium-tin-oxide (ITO) as transparent conductors. However, complicated treatments are often required to fuse crossed AgNWs to achieve low resistance and good substrate adhesion. In this work, we demonstrate a simple and effective solution method to achieve highly conductive AgNW composite films with excellent optical transparency and mechanical properties. These properties are achieved via sequentially applying TiO(2) sol-gel and PEDOT:PSS solution to treat the AgNW film. TiO(2) solution volume shrinkage and the capillary force induced by solvent evaporation result in tighter contact between crossed AgNWs and improved film conductivity. The PEDOT:PSS coating acts as a protecting layer to achieve strong adhesion. Organic photovoltaic devices based on the AgNW-TiO(2)-PEDOT:PSS transparent conductor have shown comparable performance to those based on commercial ITO substrates.