Abstract
We present a detailed first-principles analysis of the (001) surface of methylammonium lead triiodide (MAPbI3). With density functional theory, we investigate the atomic and electronic structure of the tetragonal (I4cm) phase of MAPbI3. We analyzed surface models with MAI-termination (MAI-T) and PbI2-termination (PbI2-T). For both terminations, we studied the clean surface and a series of surface reconstructions. We find that the clean MAI-T model is more stable than its counterpart, PbI2-T. For the MAI-T, reconstructions with added or removed units of nonpolar MAI and PbI2 are most stable. The corresponding band structures reveal surface states originating from the conduction band. Despite the presence of such additional surface states, our stable reconstructed surface models do not introduce new states within the bandgap.
Highlights
Perovskite solar cells (PSCs) have attracted immense attention within the photovoltaic community due to their rapidly rising power conversion efficiency (PCE): it reached 25.5%1 only nine years after the invention of the state-of-the-art PSC architecture in 2012 (PCE ∼10%).[2,3] The hybrid halide perovskite (HP) methylammonium (MA) lead triiodide (CH3NH3PbI3 or MAPbI3) has been the most common PSC photoabsorber for a long time, and it is still a major focus of both experimental and theoretical studies, along with the rising isostructural material based on formamidinium (FA)
The energy required for tetragonal MAPbI3 to decompose into methylammonium iodine (MAI) and PbI2, i.e., the difference between the left and the right values of either inequality, is as small as 0.06 eV
We consider MAI-T to be the more stable surface since the region for stable MAI-T covers a wider range of Δμk (k = Pb and I, as well as MeNH2 and H, which are not shown here)
Summary
Perovskite solar cells (PSCs) have attracted immense attention within the photovoltaic community due to their rapidly rising power conversion efficiency (PCE): it reached 25.5%1 only nine years after the invention of the state-of-the-art PSC architecture in 2012 (PCE ∼10%).[2,3] The hybrid (organic–inorganic) halide perovskite (HP) methylammonium (MA) lead triiodide (CH3NH3PbI3 or MAPbI3) has been the most common PSC photoabsorber for a long time, and it is still a major focus of both experimental and theoretical studies, along with the rising isostructural material based on formamidinium (FA). HPs have received significant recognition in luminescence and light detection.[4,5,6,7,8,9]. To advance HPs for eventual use in large-scale commercial applications, further efforts in fundamental research are still necessary to enable materials and device engineering. Researching surface passivation is critical in this regard since defects at perovskite surfaces and grain boundaries are centers of nonradiative recombination, which is a major inhibitor to further PCE improvement.[10,11,12,13,14,15,16] organic components in hybrid HPs suffer from rapid degradation when exposed to moisture, heat, and oxygen,[17–22] the effects of which can be reduced with proper surface passivation
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