Hybrid nanocrystal/polymer solar cells based on tetrapod-shaped CdSe(x)Te(1-x) nanocrystals

A series of ternary tetrapodal nanocrystals of CdSe(x)Te(1-x) with x = 0 (CdTe), 0.23, 0.53, 0.78, 1 (CdSe) were synthesized and used to fabricate hybrid nanocrystal/polymer solar cells. Herein, the nanocrystals acted as electron acceptors, and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as an electron donor. It was found that the open circuit voltage (V(oc)), short-circuit current (J(sc)) and power conversion efficiency (η) of the devices all increased with increasing Se content in the CdSe(x)Te(1-x) nanocrystals under identical experimental conditions. The solar cell based on the blend of tetrapodal CdSe nanocrystals and MEH-PPV (9:1 w/w) showed the highest power conversion efficiency of 1.13% under AM 1.5, 80 mW cm(-2), and the maximum incident photon to converted current efficiency (IPCE) of the device reached 47% at 510 nm. The influence of nanocrystal composition on the photovoltaic properties of the hybrid solar cells was explained by the difference of the band level positions between MEH-PPV and the nanocrystals.

The effect of broken conjugation on the excited state: Ether linkage in the cyano-substituted poly(p-phenylene vinylene) conjugated polymer poly(2,5,2′,5′-tetrahexyloxy-8,7′-dicyano-di-p-phenylene vinylene)

We investigate the effect of broken conjugation on the excited state dynamics of excimers in cyano-substituted phenylene-vinylene polymers. We compare previous studies on the well-characterized poly(2,5,2',5'-tetrahexyloxy-8,7'-dicyano-di-p-phenylene vinylene) (CN-PPV) with poly[oxa-1,4-phenylene-1,2-(1-cyano)-ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)-ethenylene-1,4-phenylene] (CN-ether-PPV), in which the conjugation is disrupted by the insertion of an oxygen atom within the polymer backbone. Despite the broken conjugation, the spectroscopic behavior of the two materials is similar, indicating that the cyano group dominates the photophysics in these materials. The emission in CN-ether-PPV is due to a single-chain exciton in solution and due to an interchain excimer in thin film, as previously reported for CN-PPV; however, the excimer absorption and emission in thin film are blueshifted by approximately 0.2 eV relative to CN-PPV, implying that the excimer in CN-ether-PPV is less stable. Furthermore, substitution of an ether group along the chain results in decay times in both solution and film that are twice as long than in CN-PPV due to the broken conjugation which restricts the exciton within a conjugation segment and reduces its access to internal quenching sites. These properties result in a decay time of 14 ns for CN-ether-PPV film, one of the longest decay times observed in a conjugated polymer film. The long lifetime indicates a large exciton diffusion length, making these species particularly vulnerable to quenching by other materials. This work has implications for the design of conjugated polymers for efficient optoelectronic devices, such as photovoltaics.

Synthesis of Fullerene Adducts with Terpyridyl- or Pyridylpyrrolidine Groups intrans-1 Positions

Two C(60) hexakis-adducts (2 and 3) were synthesized by using a protection-deprotection strategy. The symmetric fullerene tetrakis-adduct 8 was obtained by anthracene removal from the hexakis-adduct 7. Reaction of 8 with terpyridylglycine or pyridylglycine afforded two hexakis-adducts, 2 and 3. By using the retro-cyclopropanation reaction, the four malonate addends located on the equatorial belt of the hexakis-adducts were removed to afford two trans-1 bis-adducts, 4 and 5, with terpyridyl- or pyridylpyrrolidine groups. The structures of 2 and 3 were confirmed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and (1)H, (13)C, and COSY NMR, and UV-visible spectroscopy. The cyclic voltammograms of fullerene multiadducts 2, 3, and 9 show irreversible reductions. Self-assembled monolayers (SAMs) of 1 and 3 were formed on gold surfaces through nitrogen adsorption. SAMs of 3 represent the first example of a fullerene hexakis-adduct formed on gold surfaces through nitrogen adsorption. Controlled potential electrolyses (CPE) were conducted to prepare trans-1 bis-adducts 4 and 5 modified with terpyridyl and pyridyl groups.

Optical properties and photonic devices of doped carbon nanotubes

Chemical doping of carbon nanotubes provides a variety of opportunities for tailoring the physical properties of carbon nanotubes. In this review, we discussed the optical properties of doped carbon nanotubes and the related applications as nanoscale photonic devices. The fundamental optical properties of carbon nanotubes with various chemical doping have been summarized. Novel optoelectronic and photonic devices based on doped carbon nanotubes, such as optical nonlinear materials, optical limiting devices, photovoltaic devices, etc., have been discussed.

Organic solar cells: an overview focusing on active layer morphology

Solar cells constructed of organic materials are becoming increasingly efficient due to the discovery of the bulk heterojunction concept. This review provides an overview of organic solar cells. Topics covered include: a brief history of organic solar cell development; device construction, definitions, and characteristics; and heterojunction morphology and its relation to device efficiency in conjugated polymer/fullerene systems. The aim of this article is to show that researchers are developing a better understanding of how material structure relates to function and that they are applying this knowledge to build more efficient light-harvesting devices.

Classification of the hydrogen-bonding species in a series of novel hydrazide based azobenzene derivatives investigated by two-dimensional correlation infrared spectroscopy and molecular modeling

Classification of hydrogen-bonding species in a series of novel hydrazide modified p-methoxyazobenzene derivatives, 4-{n-[4-(4-methoxy-phenylazo)-phenoxy]-alkoxy}-benzoic acid hydrazide (Dn, n = 3, 6, 10) are performed in the present study. Temperature-dependent infrared (IR) spectra of Dn have been measured to investigate the thermal stability of the weak intermolecular interactions, such as hydrogen bonding among hydrazide moieties, pi-pi stacking among aromatic groups, and hydrophobic interaction between alkyl chains. In order to reveal the hydrogen bonding formed between NH, NH2, and CONH groups efficiently, two-dimensional (2D) correlation spectra have been constructed in the thermal sensitive spectral regions of (a) 3500-3100 cm(-1) and (b) 1700-1450 cm(-1), separately, and it have also been constructed between these two spectral regions. Based on the experimental data, the ab initio computational models have been developed to the proposed patterns of hydrogen bonding related to intermolecular interactions in Dn. The intermolecular hydrogen bondings and molecular alignments patterns result from both the experimental data and the computational models are performed for D3, D6, and D10, respectively, in the present study.

Radical ion pair mediated triplet formation in polymer–fullerene blend films

Efficient triplet formation is observed for films of high ionisation potential polythiophenes blended with a fullerene derivative, and assigned to formation via geminate charge recombination of bound radical ion pair states.

Efficient photocurrent generation by SnO2electrode modified electrophoretically with composite clusters of porphyrin-modified silica microparticle and fullerene

A silica microparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode which exhibits efficient photocurrent generation.