Formamidinium + Cesium Lead Triiodide Perovskite Thin Films: Optical Properties and Devices

Optical characterization and simulations have been applied to study formamidinium + cesium lead triiodide (FA1
_X
CsXPbI
₃
) perovskite thin films and solar cells. Near infrared to ultraviolet complex index of refraction (N = n + ik) spectra of varying cesium-to-formamidinium ratios in solution processed perovskite thin films have been extracted. Critical point transitions and the absorption onset are extracted, with x = 0.2 showing the sharpest absorption edge and least contribution from defects to absorption near the band edge. External quantum efficiency simulations of perovskite based solar cells using optical properties as input are performed and compared to experimental device results.