Abstract
CsSnI3 is a potential lead-free inorganic perovskite for solar energy applications due to its nontoxicity and attractive optoelectronic properties. Despite these advantages, photovoltaic cells using CsSnI3 have not been successful to date, in part due to low stability. We demonstrate how gradual substitution of Rb for Cs influences the structural, thermodynamic, and electronic properties on the basis of first-principles density functional theory calculations. By examining the effect of the Rb:Cs ratio, we reveal a correlation between octahedral distortion and band gap, including spin–orbit coupling. We further highlight the cation-induced variation of the ionization potential (work function) and the importance of surface termination for tin-based halide perovskites for engineering high-performance solar cells.
Highlights
Organic−inorganic hybrid halide perovskite materials have been intensively investigated in recent years.[1−11] The efficiency of solar cells made up of these materials has shown a drastic increase from 3.8% in 2009 to 22.1% in 2016.1,2 Despite the high efficiency of perovskite solar cells, two concerns hinder these materials from being an ideal solar cell technology
For the SnI2-terminated surface of the RbxCs1−xSnI3 solid solution, we find that the EVBM is predicted to decrease marginally, whereas the ECBM will shift to higher energies with an increasing value of x
We demonstrated that the RbxCs1−xSnI3 alloy becomes stable by configurational entropy and follows Vegard’s law well in terms of lattice constants, distortion angles, and band gap
Summary
Organic−inorganic hybrid halide perovskite materials have been intensively investigated in recent years.[1−11] The efficiency of solar cells made up of these materials has shown a drastic increase from 3.8% in 2009 to 22.1% in 2016.1,2 Despite the high efficiency of perovskite solar cells, two concerns hinder these materials from being an ideal solar cell technology. One issue is the presence of an organic cation (e.g., CH3NH3+), which is regarded as a principal cause of low thermal compositional stability. Replacing the organic by inorganic cations has been suggested as a way to improve thermal stability.[12] The other concern is the presence of lead (Pb), which is well-known for its toxicity. CsSnI3, a tin-based lead-free inorganic halide perovskite, is a p-type semiconductor with a high hole mobility. It has a band gap of 1.3 eV, low exciton binding energy of 18 meV, and high optical absorption coefficient of 104 cm−1, which are favorable properties for a light-absorbing material in solar cells.[15−17]
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