Quasiparticle GW Calculations on Lead-Free Hybrid Germanium Iodide Perovskite CH₃NH₃GeI₃ for Photovoltaic Applications

Abstract

Lead-free organic–inorganic halide perovskites have gained much attention as nontoxic alternatives to CH 3 NH 3 PbI 3 in next-generation solar cells. In this study, we have examined the geometric and electronic properties of methylammonium germanium iodide CH 3 NH 3 GeI 3 using density functional theory. Identifying a suitable functional to accurately model the germanium halide perovskites is crucial to allow the theoretical investigation for tuning the optoelectronic properties. The performance of various functionals (PBE, PBE+D3, PBEsol, PBEsol+D3, HSE06, and HSE06+D3) has been evaluated for modelling the structure and properties. The calculation of electronic properties was further refined by using the quasiparticle GW method on the optimized geometries, and that has an excellent agreement with the experiment. We report from our GW calculations that the characteristic of the density of states for CH 3 NH 3 GeI 3 resembles the density of states for CH 3 NH 3 PbI 3 and the effective masses of the charge carriers of CH 3 NH 3 GeI 3 are comparable to the effective masses of CH 3 NH 3 PbI 3 as well as silicon used in commercially available solar cells.

The Cs2AgRhCl6 Halide Double Perovskite: A Dynamically Stable Lead-Free Transition-Metal Driven Semiconducting Material for Optoelectronics

“…et al, 2017), whereas the experimental value for which is 1.90 eV (Stoumpos et al, 2015). There is also precedence that the inclusion of dispersion correction further reduces the bandgaps, and this is likely the case with the GGA and HSE06 methods (Umadevi and Watson, 2019). The bandgaps found in the current study for A 2 AgRhCl 6 are smaller/larger than, or comparable to, those of 2.19, 2.77, 2.33, and 3.00 eV reported for Cs 2 AgBiCl 6 , Cs 2 AgBiBr 6 , MAPbBr 3 and MAPbCl 3 (MA = methyl ammonium), respectively (Mcclure et al, 2016).…”

“…The large difference between the GGA/meta-GGA and GW/HSE06 bandgaps is not very surprising given that the former ones generally underestimate bandgaps for single and double perovskite semiconductors (Ganose et al, 2017;Umadevi and Watson, 2019). For example, the reported PBE bandgap for Cs 2 AgInCl 6 is 0.95 eV (Kumar et al, 2020), compared to the experimental value of 3.3 eV (Volonakis et al, 2017).…”

“…The three different DFT functionals employed for the relaxation of the geometry of A 2 AgRhCl 6 were SCAN-rVV10 (Sun et al, 2015;Sun J. et al, 2016;Buda et al, 2017), PBE (Perdew et al, 1996) and PBEsol (Perdew et al, 2008). The reason for choosing three functionals is that we were interested in determining the extent to which the latter two functionals underestimate the bandgaps of the systems under investigation compared to SCAN-rVV10, since they generally underestimate the bandgap of halide single and double perovskites compared to both experiment and the computationally expensive GW and HSE06 (Volonakis et al, 2017;Lamba et al, 2019;Umadevi and Watson, 2019;Wang H.-C. et al, 2019). We note that the newly-proposed SCAN-rVV10 functional is one of the strongly constrained and appropriately normed metageneralized gradient approximation (meta-GGA) functionals that is considered to model well metallic, insulating and semiconducting materials (Sun et al, 2015;Sun J. et al, 2016;Buda et al, 2017).…”

Theoretical Progress on the Relationship between the Structures and Properties of Perovskite Solar Cells

“…Pb-free perovskites, resulting from substitution of the toxic Pb at the B site, have been recently summarized on several review articles. [41,[167][168][169] Two ways are used for substitution of Pb: one is the substitution by divalent metals such as Sn, [170][171][172] Ge, [173] Cu(II), and the other is the heterovalent substitution by B(I)/B(III) pairs (B(I) = Cu(I), Ag, [174] In; [175] B(III) = Bi, Sb [175] ). The non-toxic perovskites containing two kind of B atoms could be double perovskites, and even more multiple perovskites.…”

Germanium‐Based Halide Perovskites: Materials, Properties, and Applications

“…[18] The authors applied range of theoretical methods confirming the direct nature of the MAGeI3 band gap, while the density-ofstates (DOS) analysis indicates that the valence band is predominantly made up of I(p) states and the conduction band consists primarily of Ge(p) states. [18] Moreover, an agreement between the DOS characteristics and charge carrier effective masses between MAGeI3 and MAPbI 3 was reported. [18] Finally, numerical simulations of PCS performances based on MAGeI3 have been reported by Kanoun and co-workers, with the aim of providing a guide to improve the Ge-based perovskite device efficiency.…”