ABSTRACT
Hybrid organic-inorganic perovskites are one of the promising candidates for the next-generation semiconductors due to their superlative optoelectronic properties. However, one of the limiting factors for potential applications is their chemical and structural instability in different environments. Herein, the stability of (FAPbI3 )0.85 (MAPbBr3 )0.15 perovskite solar cell is explored in different atmospheres using impedance spectroscopy. An equivalent circuit model and distribution of relaxation times (DRTs) are used to effectively analyze impedance spectra. DRT is further analyzed via machine learning workflow based on the non-negative matrix factorization of reconstructed relaxation time spectra. This exploration provides the interplay of charge transport dynamics and recombination processes under environment stimuli and illumination. The results reveal that in the dark, oxygen atmosphere induces an increased hole concentration with less ionic character while ionic motion is dominant under ambient air. Under 1 Sun illumination, the environment-dependent impedance responses show a more striking effect compared with dark conditions. In this case, the increased transport resistance observed under oxygen atmosphere in equivalent circuit analysis arises due to interruption of photogenerated hole carriers. The results not only shed light on elucidating transport mechanisms of perovskite solar cells in different environments but also offer an effective interpretation of impedance responses.
ABSTRACT
Lithium-rich antiperovskites (APs) have attracted significant research attention due to their ionic conductivity above 1 mS cm-1 at room temperature. However, recent experimental reports suggest that proton-free lithium-rich APs, such as Li3OCl, may not be synthesized using conventional methods. While Li2OHCl has a lower conductivity of about 0.1 mS cm-1 at 100 °C, its partially fluorinated counterpart, Li2(OH)0.9F0.1Cl, is a significantly better ionic conductor. In this article, using density functional theory simulations, we show that it is easier to synthesize Li2OHCl and two of its fluorinated variants, i.e., Li2(OH)0.9F0.1Cl and Li2OHF0.1Cl0.9, than Li3OCl. The transport properties and electrochemical windows of Li2OHCl and the fluorinated variants are also studied. The ab initio molecular dynamics simulations suggest that the greater conductivity of Li2(OH)0.9F0.1Cl is due to structural distortion of the lattice and correspondingly faster OH reorientation dynamics. Partially fluorinating the Cl site to obtain Li2OHF0.1Cl0.9 leads to an even greater ionic conductivity without impacting the electrochemical window and synthesizability of the materials. This study motivates further research on the correlation between local structure distortion, OH dynamics, and increased Li mobility. Furthermore, it introduces Li2OHF0.1Cl0.9 as a novel Li conductor.
