Beneficial roles of nanostructures in enhanced optical absorption and photo-carrier collection

Eunah Kim¹, Soyeong Kwon¹, Bo Ra Kim¹, Jungeun Song¹, Dong-Wook Kim^1*

¹Department of Physics, Ewha Womans University, Seoul 03760, Korea

* Presenter:Dong-Wook Kim

Nanostructure-based optoelectronic devices have attracted growing research attention to improve the performance and enable new functionalities. We prepared P3HT-coated Si-nanopillar (NP) arrays and studied spatial distribution of the surface photovoltage (SPV) in the samples using Kevin probe force microscopy.[1] The Si-NPs with high aspect ratio exhibited broadband and omnidirectional antireflection effects. Furthermore, large SPV values appeared in the P3HT layers near the Si NPs under illumination of visible light. The optical resonance strongly concentrated incident light in the Si NPs due to the graded refractive index and Mie scattering, which increased the local density of the photo-generated carriers near the NPs. We also studied the optical characteristics of 2D MoS2 layers conformally coated on 3D Si-based nanostructured substrates. The photoluminescence and Raman intensities of the MoS2 monolayers on SiO2 nanocones (NCs) are much greater than those on Si NCs. The weak light confinement in low refractive index SiO2 NC led to a large surface electric field intensity and increased the absorption of the MoS2 monolayers.[2] The photocurrent in MoS2 monolayers on nanorugged substrates showed drastic increase compared with those on planar counterparts, which indicated the suppressed recombination loss induced by local strain.[3] Our works have demonstrated that the Si-based nanostructures, fabricated by well-established fabrication techniques, are very helpful to improve not only the light trapping capability but also the carrier collection efficiency of the thin active layers grown on them.

[1] E. Kim et al., Sci. Rep. 6, 29472 (2016).
[2] E. Kim et al., Nanoscale 10, 18920 (2018).
[3] T. K. Nguyen et al., ACS Appl. Mater. Interfaces DOI: 10.1021/acsami.8b15673 (2018).

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