The atomic structure, band gap, and electrostatic potential at the (112)[1(1)over-bar0] twin grain boundary of CuInSe2

To develop a higher efficiency thin-film compound photovoltaic (PV) cell, it is crucial to understand not only the key factors determining the stability of the grain boundary (GB) but also the band gap and band bending at the GB in the photoabsorption layer. In this study, we investigate the atomic structure, band gap, and electrostatic potential at the (112)[1 (1) over bar0] twin GB of CuInSe2 (CIS), which is typically used in the photoabsorption layer in thin-film compound PV cells. We utilize aberration-corrected scanning transmission electron microscopy and first-principles hybrid-functional calculations. We find that the formation energies of the twin GB in CIS are very small: 0.03-0.15 J/m(2). The local coordination of the Se at the GB is a primary factor modulating the GB energy, band gap, and the electrostatic potential at the GB. (C) 2014 AIP Publishing LLC.