Optoelectronic Properties of (CH₃NH₃)₃Sb₂I₉ Thin Films for Photovoltaic Applications

TLDR

The study presents solution‑based fabrication and characterization of the lead‑free perovskite‑related methylammonium antimony iodide (CH₃NH₃)₃Sb₂I₉ compound. The authors fabricate amorphous (CH₃NH₃)₃Sb₂I₉ thin films by solution processing, characterize them with photothermal deflection spectroscopy and photoluminescence, and assemble a planar heterojunction solar cell incorporating the absorber. The amorphous (CH₃NH₃)₃Sb₂I₉ films exhibit a peak absorption coefficient of ~10⁵ cm⁻¹, a 2.14 eV band gap, no exciton peak, a 1.58 eV photoluminescence emission, and a 62 meV Urbach tail, while a planar heterojunction device achieves a 0.5 % power‑conversion efficiency with 55 % fill factor and 890 mV open‑circuit voltage, indicating the material is a viable starting point for Sb‑based lead‑free perovskite solar cells.

Abstract

We present solution-based fabrication and characterization of the lead-free perovskite-related methylammonium antimony iodide (CH3NH3)3Sb2I9 compound. By photothermal deflection spectroscopy (PDS), we determined a peak absorption coefficient α ≈ 105 cm–1 and an optical band gap of 2.14 eV for amorphous films of (CH3NH3)3Sb2I9. Compared to the related Bi compound, the Sb-perovskite shows no exciton peak in its absorption spectrum. The photoluminescence emission (PL) is observed at 1.58 eV, and the Urbach tail energy of this amorphous compound is Eu = 62 meV, indicating a substantial amount of energetic disorder. We fabricate a planar heterojunction solar cell with a (CH3NH3)3Sb2I9 absorber layer that yields a power conversion efficiency of η ≈ 0.5%, already featuring a decent fill factor (FF) of 55% and open-circuit voltage of 890 mV but low photocurrent densities. The result of this basic study on (CH3NH3)3Sb2I9 shows that this compound is a possible starting point for further research into Sb-based lead-free perovskite solar cells.