Effects of the number of layers on the vibrational, electronic and optical properties of alpha lead oxide

TL;DR

This study uses first principles calculations to explore how the number of layers affects the vibrational, electronic, and optical properties of alpha lead oxide, revealing potential for solar cell applications.

Contribution

The paper provides a detailed analysis of layer-dependent properties of alpha lead oxide, highlighting its suitability for solar energy devices and ease of exfoliation.

Findings

Monolayer PbO has a direct band gap of 2.59 eV.

Multilayer and bulk PbO overlap well with the solar spectrum.

Ultrathin PbO films are promising for solar cell applications.

Abstract

We have investigated the effects of number of layers on the structural, vibrational, electronic and optical properties of $\alpha$-PbO using first principles calculations. Our theoretical calculations have shown that four Raman active modes of $\alpha$-PbO tend to red-shift from bulk to monolayer due to decreasing of force constants and increasing of bond lengths. It has been shown that while bulk and multilayer $\alpha$-PbO have an indirect band gap, monolayer form has a direct band gap value of 2.59 eV. Although lead atoms have 5d states, spin-orbit coupling does not significantly affect the band structure of $\alpha$-PbO. The computed cleavage energy value (0.67 J/m$^2$) confirms that monolayer PbO can be easily obtained from its bulk counterpart by exfoliation methods. In addition to the band structure, we also calculated the optical properties and absorbed photon flux $J_{abs}$ of $\alpha$-PbO structures to investigate the possibility of solar absorption. Our calculations reveal that while monolayer and bilayer PbO have relatively larger band gaps and lower absorption coefficients, their $J_{abs}$ values are not ideal for solar absorption devices. In contrast, the multilayer and bulk phases of the $\alpha$-PbOs show good overlap with the solar spectrum and yield high electrical current values. Our calculations have indicated that ultrathin films of $\alpha$-PbO (such as 3nm thickness) could be excellent candidates for solar cells. We believe that our work can be utilized to improve electronic and optical devices based on lead oxide structures.