Ching-Yen Wei

Polymer solar cells

nature photonics | VOL 6 | MARCH 2012 | www.nature.com/naturephotonics 153 Harnessing solar energy is one of the most promising ways to tackle today’s energy issues. Although the present dominant photovoltaic (PV) technology is based on inorganic materials, high material and manufacturing costs limit its wide acceptance1. Intensive research has been conducted towards the development of low-cost PV technologies, of which organic photovoltaic (OPV) devices are one of the promising. OPV devices are based on organic semiconductors — carbon-based materials whose backbones are comprised mainly of alternating C–C and C=C bonds. Electron delocalization along the conjugated backbone is responsible for the semiconducting properties of OPV devices2. One of the major differences between organic semiconductors and inorganic semiconductors is the presence of tightly bonded excitons (electron–hole pairs) resulting from their low dielectric constant (εr ≈ 2–4). The binding energy of the Frenkel exciton is in the range of 0.3–1 eV (refs 2,3). Such a large binding energy prevents exciton dissociation by an electrical field (a non-radiative decay channel) and can achieve a high electroluminescent efficiency in organic light-emitting devices. The weak intermolecular van de Waals interaction enables the realization of low-cost, large-area deposition technologies such as roll-toroll printing3. In recent years, organic electronic devices such as organic light-emitting diodes (OLEDs), organic thin film transistors, OPVs and organic memory devices have attracted considerable attention, owing to their potential low cost and high performance characteristics. OLED displays have gained a considerable share in the portable electronics market, for use in devices such as smart phones. However, research into OPV cells continues to lag behind, despite the first patent4 and the first paper5 by Tang appearing ahead of those of OLEDs, probably owing to the fact that developing alternative energy sources has been viewed, until recently, as being relatively unimportant. OPVs are divided into two different categories according to whether their constituent molecules are either small or large (polymers). These two classes of materials are rather different in terms of their synthesis, purification and device fabrication processes. Polymer solar cells (PSCs) are processed from solution in organic solvents, whereas small-molecule solar cells are processed mainly using thermal evaporation deposition in a high-vacuum environment. Using the solution process to fabricate small-molecule solar cells has recently been gaining momentum6, although the film quality and crystallization is expected to be an issue. PSCs are attractive owing to a number of advantageous features7, including their thin-film architecture and low material consumption resulting from a high absorption coefficient, their use of organic polymer solar cells

Cu(I) chelated poly-alkoxythiophene enhancing photovoltaic device composed of a P3HT/PCBM heterojunction system

We report the Cu+ chelated poly-alkoxythiophene (P3MEET) enhancement of a solar cell device consisting of a P3HT/PCBM heterojunction system. Compared to the reference P3HT/PCBM system, a consistent increase of conversion efficiency of 0.9% via an apparent increase of incident-photon-to-current conversion efficiency (IPCE) is achieved upon optimizing the ratio of P3MEET-Cu+ : P3HT : PCBM to 1 : 9 : 6 by weight, in which 7.5 mol% of CuBr is added upon synthesizing P3MEET-Cu+. The results, in combination with relevant data gathered from atomic force microscopy, cyclic voltammetry, and electrochemical impedance spectra, lead us to conclude that the match in redox potential and increase of ordering of the film upon doping P3MEET-Cu+ play two key roles in enhancing the performance.

Design and Synthesis of Trithiophene-Bound Excited-State Intramolecular Proton Transfer Dye: Enhancement on the Performance of Bulk Heterojunction Solar Cells

In an aim to harvest UV-near-visible (360-440 nm) photons as well as to increase the morphology in the bulk heterojunction solar cells, we report herein the strategic design, synthesis, and characterization of a novel excited-state intramolecular proton-transfer dye, 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT), which bears two key functional groups, namely 3-hydroxychromone chromophore and trithiophene backbone and is then exploited into the blends of regioregular poly(3-hexylthiophene) (RR-P3HT) and phenyl-C(61)-butyric acid methyl ester (PCBM). FT acts as an excellent UV-near visible absorber, which then undergoes excited-state intramolecular proton transfer, giving rise to an orange-red proton-transfer emission that was reabsorbed by P3HT via a Forster type of energy transfer. Introduction of FT to P3HT/PCBM blend films also improves the morphology of phase separated structure, in particular, enhances the interaction of P3HT chains and the hole mobility. In this work, under the optimized condition of P3HT: PCBM:FT of 15:9:2 in weight ratio, the best performance of the device B-FT2 revealed consistent enhancements in the efficiency (eta) 4.28% and short-circuit current (J(sc)) 12.53 mAcm(-2), which are higher than that (3.68% and 10.28 mAcm(-2)) of the best performance of the control device B (P3HT:PCBM 15:9 in weight ratio) by 16 and 22%, respectively.

7-Azamelatonin: efficient synthetic routes, excited-state double proton transfer properties and biomedical implications.

On the basis of a seven‐step synthetic route, the total synthesis of 7‐azamelatonin, an analogue of melatonin, has been achieved with an overall yield of ∼9.2 %. In aqueous solution, 7‐azamelatonin exhibits a unique excited‐state double proton transfer (ESDPT) property, resulting in dual emission bands (405 and 560 nm). The ESDPT property makes 7‐azamelatonin superb as a potential molecular probe for future bioapplication and for pharmacological research.

Photodissociation of I2 in solution: the observation of solvent-dependent near-infrared emission associated with I()–solvent interaction

Abstract The photolysis of molecular iodine in solution phase has been investigated by Fourier transform techniques coupled with an ultrasensitive near-infrared detecting system. The spectral features and relaxation dynamics of the resulting 1200–1600 nm emission revealed strong solvent dependence. Detailed analyses conclude that the emitting species are attributed to the iodine atom ( 2 P 1/2 → 2 P 3/2 ) magnetic dipole transition in the near infrared perturbed by iodine atom–solvent complexes.