Phosphorene and Doped Monolayers Interfaced TiO$_2$ with Type-II Band Alignments: Novel Excitonic Solar Cells

TL;DR

This paper theoretically designs phosphorene-based heterostructures with TiO2 for excitonic solar cells, demonstrating high efficiency, ultrafast charge transfer, and potential for improved optoelectronic applications.

Contribution

It introduces novel phosphorene/TiO2 heterostructures with doped monolayers, showing enhanced light absorption and charge separation for high-efficiency excitonic solar cells.

Findings

High power conversion efficiencies comparable to MoS2/WS2 XSCs.

Ultrafast electron transfer times of 6.1–10.8 fs.

Quantum efficiency for charge separation exceeds 98%.

Abstract

Phosphorene, a new elemental two dimensional (2D) material recently isolated by mechanical exfoliation, holds the feature of a direct band gap of around 2.0 eV, overcoming graphene's weaknesses (zero band gap) to realize the potential application in optoelectronic devices. Constructing van der Waals heterostructures is an efficient approach to modulate the band structure, to advance the charge separation efficiency, and thus to optimize the optoelectronic properties. Here, we theoretically investigated three type-II heterostructures based on perfect phosphorene and its doped monolayers interfaced with TiO$_2$(110) surface. Doping in phosphorene has a tunability on built-in potential, charge transfer, light absorbance, as well as electron dynamics, which helps to optimize the light absorption efficiency. Three excitonic solar cells (XSCs) based on the phosphorene$-$TiO$_2$ heterojunctions have been proposed, which exhibit high power conversion efficiencies dozens of times higher than conventional solar cells, comparable to MoS$_2$/WS$_2$ XSC. The nonadiabatic molecular dynamics within the time-dependent density functional theory framework shows ultrafast electron transfer time of 6.1$-$10.8 fs, and slow electron$-$hole recombination of 0.58$-$1.08 ps, yielding $>98\%$ quantum efficiency for charge separation, further guaranteeing the practical power conversion efficiencies in XSC.