[13p-2V-1~11] 12.5 Organic solar cells

[13p-2V-2] Optical absorption and ionization potential of CdSe quantum dots adsorbed on ZnO single crystals

〇Taro Toyoda^1,4, Witoon Yindeesuk¹, Keita Kamiyama², Shuzi Hayase^3,4, Qing Shen^1,4 (1.Univ. Electro-Commun., 2.Bunkouokeiki, 3.Kyushu Inst. Tech., 4.JST-CREST)

Keywords:semiconductor quantum dot,ZnO single crystal,ionization potential

Semiconductor quantum dots (QDs) have been studied for their light harvesting capability as sensitizers. Despite the potential advantages, a major breakthrough in conversion efficiency of QD-sensitized solar cells (QDSCs) that equals or exceeds dye-sensitized solar cells (DSSCs) has yet to be reported. The reason is that the fundamental understanding of the surface chemistry of semiconductor QD is lacking. We describe the adsorption and growth of CdSe QDs on single crystals of ZnO with different crystal orientations. We used photoacoustic (PA) spectroscopy for the optical absorption. Photoelectron yield (PY) spectroscopy was applied to characterize the valence band maximum (VBM) of the single crystal ZnO and LUMO of CdSe QDs. The rate of adsorption is different for each crystal orientation. The QD crystals grow higher on (0001) surfaces than on (10) and (11) surfaces. The position of VBM for (0001) surface is similar to those for the (10) and (11) surfaces. The increase in the average diameter of CdSe QDs with adsorption time is independent of the crystal orientation of ZnO. The HOMO energy of CdSe QDs adsorbed on ZnO increases with increasing adsorption time different from that on TiO₂. The increase rate of HOMO energy depends on the crystal surface orientations.