| AVS 60th International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Monday Sessions |
| Session EN+AS+NS+SS-MoA |
| Session: | Interfacial Challenges in Nanostructured Solar Cells |
| Presenter: | G. Uchida, Kyushu University, Japan |
| Authors: | G. Uchida, Kyushu University, Japan D. Ichida, Kyushu University, Japan H. Seo, Kyushu University, Japan K. Kamataki, Kyushu University, Japan N. Itagaki, Kyushu University, Japan K. Koga, Kyushu University, Japan M. Shiratani, Kyushu University, Japan |
| Correspondent: | Click to Email |
The pressing need for massively scalable carbon-free energy sources has focused attention on both increasing the efficiency and decreasing the cost of solar cells. Quantum-dot (QD) solar cells employing multiple exciton generation (MEG) have attracted much attention as a candidate for the third generation solar cells, because MEG represents a promising route to increase solar conversion efficiencies up to about 44 % in single junction. Our interest has been concerned with QD solar cells using group IV semiconductor nanoparticles [1-4]. The main purpose of this study is to discuss characteristics of quantum efficiency of Ge QD solar cells in view of the MEG effect.
QD thin films containing Ge nanoparticles were deposited using 13.56 MHz radio-frequency (rf) magnetron sputtering process in Ar and H2 gas mixture under a high pressure condition of 1.5 Torr. The sputtering target was a poly-crystal Ge disk (1 inch) with a purity of 99.99%. The rf power was 50 W.
X-ray diffraction spectra of Ge nanoparticle films show transition from amorphous to crystalline structure by adding H2 gas, where the diffraction peaks appear at 2θ = 27o, 45o, and 53o corresponding to the (111), (220), and (311) crystal planes of Ge, respectively. Then, optical property of the films was investigated to reveal effects of crystalline Ge nanoparticles on the light absorption properties. For amorphous Ge films, absorption coefficient was 1.5 x 105 cm-1 at 840 nm, while for crystalline Ge films absorption coefficient drastically increased from 0.6 x 105 cm-1 at 840 nm to 4.9 x 105 cm-1 at 450 nm, which is close to 5-6 x 105 cm-1 at 450 nm in single crystal Ge. Finally, we fabricated Ge QD sensitized solar cells with rectification in the TiO2/Ge/polysulfide electrolyte system. The incident photo-to-current conversion efficiency increases with decreasing the wavelength, and it is 10 % at 400 nm. The result indicates that excitons generated in Ge nanoparticles were separated into electrons and holes, and such carriers successfully extracted to th e outer circuit.
[1] G. Uchida, et al., Phys. Stat. Sol. (c) 8 (2011) 3021.
[2] G. Uchida, et al., Jpn. J. Appl. Phys. 51 (2011) 01AD01.
[3] H. Seo, et al., Electrochim. Atca 87 (2013) 213.
[4] H. Seo, et al., Electrochim. Atca 95 (2013) 43.