Room temperature optical properties of organic–inorganic lead halide perovskites

• Dielectric functions of CH3NH3PbI3−xClx and CH3NH3PbI3 perovskites are reported.
• Relatively low infrared refractive index values (2.10–2.25) are determined.
• ε∞ for both CH3NH3PbI3−xClx and CH3NH3PbI3 is lower than generally assumed.
• Absorption coefficients deduced from these data lie at midrange of published work.
• Values for CH3NH3PbI and CH3NH3PbI3−xClx agree within measurement uncertainties.

Past two years have seen the rapid emergence of a new class of solar cell based on mixed organic–inorganic halide perovskites. The optical and optical frequency dielectric properties of these perovskites at ambient temperatures are important both to the design of optimised solar cells and in other areas such as the refinement of electronic band structure calculations. Limited previous information has been published. The experimental optical and related dielectric constants of CH3NH3PbI3−xClx and CH3NH3PbI3 perovskite films are reported at 297 K as determined by detailed analysis of reflectance and transmittance data. Absorption coefficients are also extracted from these data and compared with a range of previously reported values.