Bandgap Assessment of Compositional Variation for Uncovering High‐Efficiency Improved Stable All‐Inorganic Lead‐Free Perovskite Solar Cells

Abstract

The quest for suitable material technology becomes an imperative aspect of PV energy conversion applications. Pursuing ideal materials or designing efficient PV devices requires a keen understanding of underlying PV action and material properties. These include defect-free, chemically and mechanically stable, semiconductive, and absorption properties, which could be easily tuned, manipulated, and readily fabricated. The candidate for such a futuristic material could be a perovskite solar cell (PSC), which has a dramatically improved performance over the last decade. [4] Recent reports observed a steep rise in efficiency from %3% to %25.5% for Pb-based hybrid perovskites (a combination of MAPbI 3 and FAPbI 3 ). [5][6][7][8] These hybrid compositions of PSC are susceptible to long-term stability issues due to temperature, moisture exposure cycle, lead (Pb)based toxicity, and I-V hysteresis characteristics, which limit or question their practical use. [9][10][11] Therefore, the significant research gap is to find practical solutions to the Pb-toxicity and stability issue while preserving or improving the inherent performance and remarkable photophysical properties. Stability issues in hybrid organic-inorganic perovskite are severe limiting issues, mainly due to hygroscopicity, volatility, and thermal and chemical instability of organic cations. It is likely resolved by replacing the organic part with inorganic-based perovskite. [12] For addressing stability issue, organic cations such as CH 3 NH 3 þ (methylammonium, MA) and (HC(NH 2 ) 2 þ (formamidium, FA) are substituted with inorganic cations such as Cs and Rb. For addressing Pb toxicity issues, Pb is substituted with same group elements Sn and Ge. [13][14][15][16][17][18] The fully inorganic perovskite are continually explored to identify suitable replacements for Pb toxicity and MA stability issues while maintaining perovskite's superior optical properties. The inorganic absorberbased devices of CsPbI 3 have shown efficiency of 20%. [19] These inorganic absorbers perform comparatively with original hybrid organic-inorganic (MAPbI 3 , FAPbI 3 ) perovskites; however, it does not answer the lead presence issue. Sn-replaced Pb perovskites have shown high absorption and optical properties, optimal bandgap, and efficiency around 10% in FASnI 3 devices. This Sn substitution solves the Pb toxicity issues; however, Sn readily goes under oxidation from Sn þ2 to Sn þ4 , which rapidly degrades device performances and further aggravates the stability issues. Literature reports have shown that partial substitution

CsSn0.5Ge0.5I3‐Based Lead‐Free Highly Stable Perovskite Solar Cell: Numerical Modeling for Estimating Performance Ceiling

“…[5] The rapid and spontaneous oxidation of Sn 2þ to Sn 4þ during crystallization releases holes in the valence band, leading to strong p-type doping and destabilizing the device's p-i-n configuration. [6][7][8][9][10][11] Recent literature reports suggested that substituting Pb 2þ with mixed Ge-Sn could effectively solve the lead toxicity issue on the one hand and the long-term stability on the other. [12][13][14][15] This mixed Sn-Ge cation at the B site in ABX 3 perovskite has improved ambient, thermal, and photostability while preserving excellent photophysical and wide-bandgap tunability properties of perovskite.The peculiar, enhanced stability of tinÀgermanium Sn-Ge alloyed perovskite such as CsSn 0.5 Ge 0.5 I 3 is due to the introduction of Ge.…”

Simulation of Native Oxide‐Passivated CsSn0.5Ge0.5I3 Highly Stable Lead‐Free Inorganic Perovskite Solar Cell

“…R S should remain below 1 Ω cm 2, and R Sh must be above 1 k Ωcm 2 for efficient device functioning. The empirical relation gives the dependence of device J – V characteristic on R S and R Sh [ 24 ] V is the applied voltage, I ph is the light generated current, I s , n , K , and T are the reverse saturation current, ideality factor, Boltzmann constant, and temperature, respectively.…”

“…[16] SCAPS is a 1D Poisson solver package for simulating solar devices, available from the University of Gent, Belgium, Department of Electronics and Information Systems (ELIS), by Marc Burgelman et al [17] SCAPS-1D results have good coherence between experimental and simulation results with an error margin of less than 10 À15 . [18] It can model thin-film polycrystalline solar cells like CdTe, [19] CIGS, [20] CZTS, [21] SnS, [22] FeS 2 , [23] perovskite [24,25] etc. SCAPS solves three basic differential semiconductor equations (Poisson equation and continuity equation for both holes and electrons) at the interface/contact of the device structure.…”

“…R S should remain below 1 Ω cm 2, and R Sh must be above 1 k Ωcm 2 for efficient device functioning. The empirical relation gives the dependence of device J-V characteristic on R S and R Sh[24]…”