Nowadays, high efficiency and low cost solar cell is still technological challenging. In this study, crystalline GaAs NWs with the uniform, pure <110>, <111> orientations and other different mixture ratios can be successfully prepared by tuning the catalyst thickness, nucleation and growth temperatures in the two-step chemical vapor deposition. The single GaAs NWs are fabricated into Au-Al asymmetric Schottky contact solar cells 1 by a simple ultraviolet photolithography process. The low-cost NW solar cell shows a record high efficiency of ~16% under air mass 1.5 global (AM 1.5G) illumination, which produces another record in addition to the vertically aligned p-i-n GaAs NW solar cells previously reported (40%), where the superior photovoltaic performance is attributed to the light concentrating effect of NWs with diameter in the order of light wavelength 2. Employing lift-off resists, three-layer NW parallel arrays can be easily attained for X-ray diffraction in order to evaluate their growth orientation along with the fabrication of NW parallel arrays based Schottky photovoltaic devices for the subsequent performance assessment3. Notably, the open circuit voltage of purely <111>-oriented NW arrayed cells is far higher than that of <110>-oriented NW arrayed counterparts, which can be interpreted by the different surface Fermi level pinning existed on various NW crystal surface planes due to the different As dangling bond densities.
Fig1. (a) Output IV curve of a single GaAs NW solar cell and (b) the orientation dependent PV property of printed GaAs NW array solar cells
1. Han, N.; Yang, Z.; Wang, F.; Dong, G.; Yip, S.; Liang, X.; Hung, T. F.; Chen, Y.; Ho, J. C., High performance GaAs nanowire solar cells for flexible and transparent photovoltaics. ACS Appl. Mater. Interfaces 2015, 7, 20454-20459.
2. Krogstrup, P.; Jorgensen, H. I.; Heiss, M.; Demichel, O.; Holm, J. V.; Aagesen, M.; Nygard, J.; Morral, A. F. I., Single-nanowire solar cells beyond the Shockley-Queisser limit. Nat. Photonics 2013, 7 (4), 306-310.
3. Han, N.; Yang, Z. X.; Wang, F. Y.; Yip, S.; Li, D. P.; Hung, T. F.; Chen, Y. F.; Ho, J. C., Crystal Orientation Controlled Photovoltaic Properties of Multilayer GaAs Nanowire Arrays. ACS Nano 2016, 10 (6), 6283-6290.