Silicon clathrates for photovoltaics predicted by a two-step crystal structure search

TL;DR

This paper introduces a two-step first-principles crystal structure search to identify silicon clathrates with favorable bandgaps and absorption properties, potentially enhancing photovoltaic efficiency beyond traditional silicon.

Contribution

It presents a novel two-step computational method to discover silicon clathrates with improved photovoltaic properties, including metastable structures with near-optimal bandgaps.

Findings

Identified four metastable silicon clathrate structures with potential photovoltaic benefits.

Some structures have bandgaps close to the Shockley-Queisser limit.

Certain silicon clathrates exhibit better absorption rates than cubic diamond silicon.

Abstract

Silicon in a cubic diamond structure currently plays a significant role in the photovoltaic industry. However, the intrinsic band structures of crystalline silicon restrict its sunlight conversion efficiency. Recently, a clathrate-like Si-24 has been successfully synthesized, which has a quasi-direct bandgap and sheds light on silicon-based photovoltaics. Here, we proposed a two-step crystal structure search method based on first-principles calculations and explored silicon clathrate structures extensively. First, the guest-host compounds were searched at high pressure, and then, the porous guest-free silicon clathrates were obtained by removing the guest atoms. Using potassium as the guest atom, we identified four metastable silicon clathrate structures, and some of them have bandgaps close to the optimal range of the Shockley-Queisser limit and have a better absorption rate than the cubic diamond silicon. These silicon clathrates may have promising value in photovoltaic applications.