| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+EM+SS-ThA |
| Session: | Applications of Self-Assembled Monolayers and Layer-by-Layer Assemblies |
| Presenter: | T. Yoshimura, Tokyo University of Technology, Japan |
| Authors: | T. Yoshimura, Tokyo University of Technology, Japan S. Ishii, Tokyo University of Technology, Japan |
| Correspondent: | Click to Email |
[Introduction] We previously proposed oxide-semiconductor-based sensitized solar cells, in which polymer multiple quantum dots (MQDs) are utilized for sensitizing layers, and fabricated the polymer MQDs on glass substrates by Molecular Layer Deposition (MLD) [1]. In the present study, we grew polymer MQDs on TiO2 by MLD. The polymer MQD growth on TiO2 was confirmed by photoluminescence (PL) spectra.
[ Proposed Solar Cells S ensitized by Polymer MQDs] The proposed sensitized solar cell consists of an oxide semiconductor layer and polymer MQDs on the surface. The polymer MQD contains different-length quantum dots (QDs) in the backbone wire, and consequently, a wide absorption band is obtained by superposition of narrow absorption bands of the individual QDs. This spectral division with the narrow bands can reduce the energy loss arising from the heat generation due to excess photon energy in light absorption processes.
[Absorption/Photoluminescence Spectra of Polymer MQDs ] Reference samples of poly-azomethine (AM) and polymer MQDs: OTPTPT, OTPT, and OT were grown on glass substrates by connecting terephthalaldehyde (TPA), p-phenylenediamine (PPDA), and oxalic dihydrazide (ODH) with designated orders using MLD. The QD lengths in OTPTPT, OTPT and OT are respectively ~3, ~2 and ~0.8 nm. With decreasing the QD length, while the absorption peak shifts to high-energy side due to the quantum confinement, the PL peak shifts to low-energy side due to the Stokes shift. Namely, in the order of poly-AM to OT, the electrons become highly localized to increase the surrounding atoms’ displacement caused by the electron transitions, resulting in the Stokes shift enhancement.
[Growth of Polymer MQDs on TiO2] We performed MLD to grow poly-AM on ZnO and TiO2 powder layers. A yellow film of poly-AM was observed on TiO2. For ZnO, however, no film growth was observed because of weak hydrophilic characteristics of ZnO surfaces. We grew poly-AM and polymer MQDs of TO on the TiO2 powder layers by MLD, and measured their PL spectra. The PL spectrum of TO was located at lower-energy side than that of poly-AM, which is parallel to the tendency observed in the PL spectra of the reference samples. From this result, it is concluded that polymer MQDs can be grown on TiO2 by MLD as the sensitizing layers for solar cells.
[1] T. Yoshimura, R. Ebihara, A. Oshima, “Polymer Wires with Quantum Dots Grown by Molecular Layer Deposition of Three Source Molecules for Sensitized Photovoltaics,” J. Vac. Sci. Technol. A. 29: 051510-1-6 (2011).