Group IV clathrates: synthesis, optoelectonic properties, and photovoltaic applications

Abstract

Group IV clathrates are a unique class of guest/framework type compounds that are considered potential candidates for a wide range of applications (superconductors to semiconductors). To date, most of the research on group IV clathrates has focused heavily on thermoelectric applications. Recently, these materials have attracted attention as a result of their direct, wide band gaps for possible use in photovoltaic applications. Additionally, framework alloying has been shown to result in tunable band gaps. In this review, we discuss the current work and future opportunities concerning the synthesis and optical characterization of group IV clathrates for optoelectronics applications.

Inorganic and methane clathrates: Versatility of guest–host compounds for energy harvesting

“…The results indicated that vacancies can facilitate Na guest removal from the clathrate lattice, and guest mobility through 6-membered rings was more favorable than that through 5-membered rings of the cages. 67 It should be noted that no vacancies have been experimentally observed in this particular system, but the driving force for Na diffusion through the framework still needs to be investigated. However, transmission electron microscopy measurements have revealed other defects in the system, such as the presence of dislocations and stacking faults.…”

Silicon Clathrate Films for Photovoltaic Applications

“…Furthermore, the material presents the advantage of a direct bandgap as opposed to conventional diamond silicon . In the second case, the large size of spheres composing the Si clathrates enables a high storage capacity within the cage that can be used for lithium or sodium ion batteries. − Thermoelectric properties of clathrates also seem favorable. , Coming back to optoelectronics, Si clathrate films (SCF) have been proposed to be used in solar cells. ,,− Their main advantage compared to diamond Si is that diamond Si has an indirect bandgap of 1.1 eV and a direct bandgap of 3.4 eV which makes it a poor solar spectrum absorber. Thus, the diamond Si absorber has to be thick (100 μm) and at the same time very pure to provide a large minority carrier diffusion length .…”

Intermediate bands in type-II silicon clathrate with Cu and Ag guest atoms

“…22 In this work we focus on the type-II Si clathrate, which can be synthesized routinely 23 and has been investigated for PV applications. [15][16][17] The Si-Si bonds in type-II clathrates do not deviate much from the ideal sp 3 tetrahedral bonding in diamond Si. The average bond length is 2.34Å, 24 and bond angle is near 109.47 • .…”

“…[4][5][6] The weak interaction between guests and host facilitates tuning electronic, optical and dynamical properties of clathrates; 7 as a result, they exhibit many intriguing physical properties, such as glasslike thermal conductivity, 8 superconductivity in sp 3 covalent bonded solids 9,10 and magnetism. 11,12 Recently, Si clathrate materials have attracted intense research interest for applications including lithium ion batteries, 13 thermoelectrics, 14 photovoltaic (PV) cells and optoelectronics, [15][16][17] etc.…”