Highly Air-Stable Single-Crystalline β-CsPbI3Nanorods: A Platform for Inverted Perovskite Solar Cells

The synthesis of single-crystalline beta-CsPbI(3)perovskite nanorods (NRs) using a colloidal process is reported, exhibiting their improved photostability under 45-55% humidity. The crystal structure of CsPbI(3)NRs films is investigated using Rietveld refined X-ray diffraction (XRD) patterns to determine crystallographic parameters and the phase transformation from orthorhombic (gamma-CsPbI3) to tetragonal (beta-CsPbI3) on annealing at 150 degrees C. Atomic resolution transmission electron microscopy images are utilized to determine the probable atomic distribution of Cs, Pb, and I atoms in a single beta-phase CsPbI3NR, in agreement with the XRD structure and selected area electron diffraction pattern, indicating the growth of single crystalline beta-CsPbI3NR. The calculation of the electronic band structure of tetragonal beta-CsPbI(3)using density functional theory (DFT) reveals a direct transition with a lower band gap and a higher absorption coefficient in the solar spectrum, as compared to its gamma-phase. An air-stable (45-55% humidity) inverted perovskite solar cell, employing beta-CsPbI(3)NRs without any encapsulation, yields an efficiency of 7.3% with 78% enhancement over the gamma-phase, showing its potential for future low cost photovoltaic devices.