Proceedings of Perovskite Thin Film Photovoltaics (ABXPV17)
Publication date: 18th December 2016
Metal halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) are generating great excitement due to their outstanding optoelectronic properties, which lend them to application in high efficiency solar cells and light-emission devices. However, there is currently debate over what drives the second order electron-hole recombination in these materials. Here, we propose that the band gap in CH3NH3PbI3 has a direct-indirect character.[1] Time-resolved photo-conductance measurements show that generation of free mobile charges is higher for excitation energies just above the bandgap (1.7 eV) than further above the bandgap (>1.8 eV). Furthermore, we find that second-order band-to-band recombination of photo-excited electrons and holes is retarded when the temperature is decreased. A thermal activation energy of 47 meV is found, which is on the same order of magnitude as the difference between the direct and indirect bandgaps predicted from literature.[2] These results provide a new framework to understand the optoelectronic properties of metal halide perovskites and analyze spectroscopic data.
[1] Hutter, E. M. et al. Direct–indirect character of the bandgap in methylammonium lead iodide perovskite. Nat. Mater. 16, 115–120 (2017).
[2] Motta, C. et al. Revealing the role of organic cations in hybrid halide perovskite CH3NH3PbI3. Nat. Commun. 6, 7026 (2015).