@phdthesis{oai:uec.repo.nii.ac.jp:00000926,
 author = {Witoon, Yindeesuk},
 month = {2016-09-15},
 note = {2013, Semiconductor quantum dots (QDs) have attracted significant interest in sensitized solar cells. The semiconductor QDs exploit as a sensitizer and have several advantages such as quantum confinement, large extinction coefficient, and multiple exciton generation. A successive ionic layer adsorption and reaction (SILAR) method is an ion-by-ion growth of thin films and provides high coverage of the electrode. Therefore, the SILAR method is a fascinating process for preparation of CdSe QDs. In addition, an inverse opal TiO2 (IO-TiO2) film have a honeycomb structure with large interconnected pores that lead to a better infiltration of electrolyte in a photoelectrochemical cell.   To investigate the effect of the electrode morphology, we have studied the optical absorption properties of CdSe QDs adsorbed on IO-TiO2 and nanoparticulate TiO2 (NPTiO2) electrodes for comparison, including the photovoltaic properties of CdSe QDs sensitized solar cells (QDSSCs). CdSe QDs were grown on an IO-TiO2 and NP-TiO2 surface by a SILAR method for different cycles. A sandwich structure solar cell was consisted of Cu2S on brass as a counter electrode and a polysulfide (S/S2-) redox system as the electrolyte.   The average diameter of the QDs was estimated by applying an effective mass approximation to the optical absorption spectra. Linear dependence of the size of the QDs with increasing number of cycles was confirmed by a redshift in the optical absorption spectrum. The average diameter of the CdSe QDs on the IO-TiO2 electrodes was similar to that on the NP-TiO2 ones, indicating that growth is independent of morphology. However, there were more CdSe QDs on the NP-TiO2 electrodes than on the IO-TiO2 ones, indicating that there were different amounts of active sites on each type of electrode. In addition, the Urbach parameter (as a guide of disordered states) of the exponential optical absorption tail was also estimated from the optical absorption spectrum. The Urbach parameter of CdSe QDs on IO-TiO2 electrodes was higher than that on NP-TiO2 ones, indicating that CdSe QDs on IO-TiO2 electrodes are more disordered states than those on NP-TiO2 electrodes. The Urbach parameter decreases in both cases with the increase of SILAR cycles, and it tended to move toward a constant value. The incident photon-to-current conversion efficiency (IPCE) and photovoltaic properties of sandwich structure solar cells were studied under an illumination of air mass (AM) 1.5 using Cu2S on brass as a counter electrode and a polysulfide (S/S2-) redox system. The photosensitization of CdSe QDs on TiO2 electrodes in the visible region could be observed in both electrode morphologies. The IPCE spectra of both IO-TiO2 and NP-TiO2 cells were shifted to low photon energy region because a size of CdSe QDs on TiO2 grows with increasing SILAR cycle. The lower IPCE in IO-TiO2 cell comparison with NP-TiO2 cell could be because of a fewer adsorption of Cd2+ ions, and smaller surface area. The maximum photovoltaic conversion efficiency (η) of CdSe QDs on IO-TiO2 was 1.3% and that of CdSe QDs on NP-TiO2 was 2.7%, prepared with 9 cycles. Lower η of CdSe QDs on IO-TiO2 than that on NP-TiO2 was possibly because of the lower adsorption of Cd2+ ions, a larger amount of surface states, and lower TiO2 surface area. In this study, the series resistance (Rs) could assume that depends on the charge transfer resistance in TiO2 film adsorbed with CdSe QDs. The estimated Rs of IO-TiO2 cell is larger than NP-TiO2 one. A possible reason for the different Rs, the QDs on IO-TiO2 has fewer amounts than the QDs on NP-TiO2, which result in the QDs on IO-TiO2 has fewer injected electrons than the QDs on NP-TiO2. These results indicate that the CdSe SILAR cycle is the important condition that affects the photovoltaic properties of CdSe QDSSCs.},
 school = {電気通信大学},
 title = {Optical Absorption and Photovoltaic Properties of CdSe Quantum Dots on TiO2 Electrodes with Different Morphology},
 year = {}
}