Hot Carrier Schottky Junction Solar Cell with Metamaterial Absorber

Y. Wang, J.B. Chou, D. Fenning, Y. Shao-Horn, S.G. Kim
Sponsorship: Masdar Flagship Proposal


Hot carrier solar cells can theoretically obtain efficiencies up to 66%, substantially exceeding the Shockley-Queisser limit of a single junction cell at about 34%.[1] However, extracting hot carriers efficiently is stilla major challenge.  A common strategy to increase the efficiency of hot carrier collection is to use metallic nanoparticles or thin films.   Unfortantely, the solar broadband absorption of such films are typically very poor. Based on these points, we propose a hot carrier schottky junction solar cell with a metamaterial absorber. Our structure is a two dimensional cavity array with metal and semiconductor thin film coatings.[2] The metal-semiconductor Schottcky interface can help extract hot carriers generated in the metal and the nanocavity structure can couple with light at various wavelengths which leads to broadband absorption.


The SEM image of the device structure is shown in Figure 1.  We fabricated it with nanofabrication techniques scalable to full-size 6” Si wafers. The cavity is 1 μm deep and the diameter is about 500nm. Then we sputtered 10 nm thick Au layer and deposited 50 nm thick TiO2 by using ALD. The absorption simulation of this structure by using FDTD is shown in Figure 2. It shows that the structure can achieve high absorption (50-90%) from 200nm to 2μm. Which indicates that our device can capture light over the entire solar spectrum, and potentially convert it into hot carriers. Hot carriers generated in the Au will then transfer to the TiO2 to be collected.


Figure 1: SEM image of the two dimensional cavity array structure with thin Au and TiO2 layers on it.

Figure 2: Simulated Reflection-Transmission-Absorption spectra.


Further Reading

[1]             R. T. Ross and A. J. Nozik, “Efficiency of hot‐carrier solar energy converters,” J. Appl. Phys., vol. 53, no. 5, pp. 3813–3818, May 1982.

[2]             J. B. Chou, Y. X. Yeng, Y. E. Lee, A. Lenert, V. Rinnerbauer, I. Celanovic, M. Soljačić, N. X. Fang, E. N. Wang, and S.-G. Kim, “Enabling Ideal Selective Solar Absorption with 2D Metallic Dielectric Photonic Crystals,” Adv. Mater., p. n/a–n/a, Sep. 2014.