Vacuum‐Healing of Grain Boundaries in Sodium‐Doped CuInSe<sub>2</sub> Solar Cell Absorbers
Finn Babbe, Nicoleta Nicoara, Harvey Guthrey, Nathalie Valle, Omar Ramírez, Damien Aureau, Hossam Elanzeery, Deepanjan Sharma, José Virtuoso, Jean‐Nicolas Audinot, Anastasiya Zelenina, Sevan Gharabeiki, Tom Wirtz, Susanne Siebentritt, Phillip J. Dale, Sascha Sadewasser, Diego Colombara
Abstract
Abstract Alkali metal doping and grain boundaries (GB) have been at the center of attention within the Cu(In,Ga)(S,Se) 2 photovoltaics community for years. This study provides the first experimental evidence that the GB of sodium‐doped CuInSe 2 thin films may undertake reversible oxidation even at room temperature, whereas undoped films may not. The findings are corroborated by cathodoluminescence imaging, secondary ion mass spectrometry, and Kelvin probe force microscopy on air‐exposed films subsequently subject to vacuum. A thermochemical assessment identifies the likely solid–gas equilibria involved. These reactions open new research questions with respect to the beneficial role played by alkali metal dopants in chalcopyrite solar cells and may steer the community toward new breakthroughs.