Tsung-Wei Zeng

A large interconnecting network within hybrid MEH-PPV/TiO 2 nanorod photovoltaic devices

This is a study of hybrid photovoltaic devices based on TiO2 nanorods and poly[2-methoxy-5-(2 � -ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). We use TiO 2 nanorods as the electron acceptors and conduction pathways. Here we describe how to develop a large interconnecting network within the photovoltaic device fabricated by inserting a layer of TiO2 nanorods between the MEH-PPV:TiO2 nanorod hybrid active layer and the aluminium electrode. The formation of a large interconnecting network provides better connectivity to the electrode, leading to a 2.5-fold improvement in external quantum efficiency as compared to the reference device without the TiO2 nanorod layer. A power conversion efficiency of 2.2% under illumination at 565 nm and a maximum external quantum efficiency of 24% at 430 nm are achieved. A power conversion efficiency of 0.49% is obtained under Air Mass 1.5 illumination. (Some figures in this article are in colour only in the electronic version)

Correlating interface heterostructure, charge recombination, and device efficiency of poly(3-hexyl thiophene)/TiO2 nanorod solar cell.

The charge recombination rate in poly(3-hexyl thiophene)/TiO(2) nanorod solar cells is demonstrated to correlate to the morphology of the bulk heterojunction (BHJ) and the interfacial properties between poly(3-hexyl thiophene) (P3HT) and TiO(2). The recombination resistance is obtained in P3HT/TiO(2) nanorod devices by impedance spectroscopy. Surface morphology and phase separation of the bulk heterojunction are characterized by atomic force microscopy (AFM). The surface charge of bulk heterojunction is investigated by Kelvin probe force microscopy (KPFM). Lower charge recombination rate and lifetime have been observed for the charge carriers in appropriate heterostructures of hybrid P3HT/TiO(2) nanorod processed via high boiling point solvent and made of high molecular weight P3HT. Additionally, through surface modification on TiO(2) nan,orod, decreased recombination rate and longer charge carrier lifetime are obtained owing to creation of a barrier between the donor phases (P3HT) and the acceptor phases (TiO(2)). The effect of the film morphology of hybrid and interfacial properties on charge carrier recombination finally leads to different outcome of photovoltaic I-V characteristics. The BHJ fabricated from dye-modified TiO(2) blended with P3HT exhibits 2.6 times increase in power conversion efficiency due to the decrease of recombination rate by almost 2 orders of magnitude as compared with the BHJ made with unmodified TiO(2). In addition, the interface heterostructure, charge lifetime, and device efficiency of P3HT/TiO(2) nanorod solar cells are correlated.

Effects of bifunctional linker on the performance of P3HT/CdSe quantum dot-linker-ZnO nanocolumn photovoltaic device

We study the effects of bifunctional linker on the photovoltaic properties of P3HT/CdSe quantum dot-linker-ZnO nanocolumn heterostructure. The CdSe quantum dots are bound on the surface of ZnO nanocolumns through either aliphatic linker of 3-aminopropyl trimethoxysilane(APS) or aromatic linker of p-aminophenyl trimethoxysilane(APhS) using simple solution process. As compared to CdSe bound by aliphatic linker(APS), while CdSe is bound by aromatic linker(APhS), more than one fold increase of short circuit current density (J(SC)) of the device obtained under irradiance, which is attributed to a more efficient charge transfer dynamics at interface. In addition, the ZnO-APhS-CdSe/P3HT devices possess about 4.8 folds in power conversion efficiency as compared to ZnO/P3HT device as the results of reduction in shunt loss and interfacial recombination.

Effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure

We study the effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure. The CdSe quantum dots are anchored on the surface of ZnO nanocolumns through either aliphatic linker of 3-aminopropyl trimethoxysilane (APS) or aromatic linker of p-aminophenyl trimethoxysilane (APhS). X-ray photoelectron spectroscopy is used to confirm the bifunctional linker bound onto CdSe quantum dots and onto the ZnO nanocolumns. The TEM study reveals a CdSe quantum dot shell of about 15 nm coated on the ZnO nanocolumns. The photoluminance (PL) spectroscopy and time-resolved PL spectroscopy of ZnO nanocolumn-linker-CdSe quantum dots reflects that the photo-induced electron transfer across the interface of ZnO and CdSe through the aromatic APhS is more efficient than the aliphatic APS. This study demonstrates that through the usage of appropriate surface linker, the charge transfer rate across the interfaces of donor/acceptor (D/A) heterostructure can be improved for potential photovoltaic cell applications.

Hybrid poly(3-hexyl thiophene)–TiO2 nanorod oxygen sensor

Conjugated polymers are promising materials for oxygen sensing owing to their specific interaction with oxygen molecules and also advantages of low cost, easy processing and room temperature operation. The present work for the first time demonstrates an oxygen sensing material of poly(3-hexylethiophene) (P3HT)–TiO2 nanorod hybrid thin film which reveals considerable improvement of sensing response as compared to the pristine P3HT film. The effects of hybrid composition and film thickness on sensing performance were systematically investigated. Kelvin probe force microscopy (KPFM) was employed to understand the mechanism of oxygen sensing including the control of surface morphologies and electronic properties by TiO2 incorporation. The hybrid material developed in this study is helpful in the advancement of room temperature oxygen sensing technology.