2:15 PM - 2:45 PM
[15p-2H-2] Dynamic SPM Nanocharacterization of Next Generation Photovoltaic Cells under Visible Light Irradiation
Keywords:scanning probe microscopy,photovoltaic cell,nanocharacterization
Next generation photovoltaic cells (PV) using the nanostructure such as quantum dots or quantum wells attracts attention, but the conversion efficiency is still at a low level in comparison with theoretical prediction. Understanding of the role of quantum nanostructure in the photoelectric conversion is indispensable for device design. Therefore measurement of local electronic properties such as electric potential, electronic state, charge distribution around the excitation center, under visible light irradiation, is necessary. Conventionally local electronic properties have been indirectly guessed from macroscopic measurement such as I-V measurement, but the direct measurement with high spatial resolution is necessary to understand photoelectric translation mechanism of nanostructured PVs. In correspondence with such request, we have realized the dynamic in situ nanocharacterization techniques working in light irradiation using scanning tunnel microscopy/spectroscopy, atomic force microscopy, and Kelvin probe force microscopy. Here, we introduce a measurement example for III-V compound multiple quantum well (MQW) which is a candidate of the inter-band type PVs. Firstly, using KPFM, we introduce in situ electric potential measurements along the p-i-n junctions that we carried out by an open circuit and closed circuit configurations under light irradiation. We show that we can measure optical power dependence of the open circuit voltage by KPFM data analysis quantitatively. Then, we introduce an atomic-scale measurement example of MQW using the ultrahigh vacuum low temperature STM, including the detailed analysis of the atomic arrangement, electronic state, and band profile. We argue about the accumulation of charge in MQW based on the STM topographic measurement under an irradiation by light.