Indirect to direct bandgap transition in methylammonium lead halide perovskite. Issue 2 (23rd December 2016)

• Record Type: Journal Article
• Authors: Wang, Tianyi; Daiber, Benjamin; Frost, Jarvist M.; Mann, Sander A.; Garnett, Erik C.; Walsh, Aron; Ehrler, Bruno
• Is Part Of: Energy & environmental science. Volume 10:Issue 2(2017)
• Page Start: 509
• Page End: 515
• Publication Date: 2016-12-23
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/c6ee03474h
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : Unusually long charge carrier lifetime in methylammonium lead halide perovskites is a result of the Rashba-split indirect bandgap. At high pressure the bandgap becomes purely direct, with shorter carrier lifetime and higher radiative efficiency. Abstract : Methylammonium lead iodide perovskites are considered direct bandgap semiconductors. Here we show that in fact they present a weakly indirect bandgap 60 meV below the direct bandgap transition. This is a consequence of spin–orbit coupling resulting in Rashba-splitting of the conduction band. The indirect nature of the bandgap explains the apparent contradiction of strong absorption and long charge carrier lifetime. Under hydrostatic pressure from ambient to 325 MPa, Rashba splitting is reduced due to a pressure induced reduction in local electric field around the Pb atom. The nature of the bandgap becomes increasingly more direct, resulting in five times faster charge carrier recombination, and a doubling of the radiative efficiency. At hydrostatic pressures above 325 MPa, MAPI undergoes a reversible phase transition resulting in a purely direct bandgap semiconductor. The pressure-induced changes suggest epitaxial and synthetic routes to higher efficiency optoelectronic devices.