Simultaneous observation of free and defect-bound excitons in CH3NH3PbI3 using four-wave mixing spectroscopy

Abstract

Solar cells incorporating organic-inorganic perovskite, which may be fabricated using low-cost solution-based processing, have witnessed a dramatic rise in efficiencies yet their fundamental photophysical properties are not well understood. The exciton binding energy, central to the charge collection process, has been the subject of considerable controversy due to subtleties in extracting it from conventional linear spectroscopy techniques due to strong broadening tied to disorder. Here we report the simultaneous observation of free and defect-bound excitons in CH3NH3PbI3 films using four-wave mixing (FWM) spectroscopy. Due to the high sensitivity of FWM to excitons, tied to their longer coherence decay times than unbound electron-hole pairs, we show that the exciton resonance energies can be directly observed from the nonlinear optical spectra. Our results indicate low-temperature binding energies of 13 meV (29 meV) for the free (defect-bound) exciton, with the 16 meV localization energy for excitons attributed to binding to point defects. Our findings shed light on the wide range of binding energies (2-55 meV) reported in recent years.

References in corpus (3)

• Direct Measurement of the Exciton Binding Energy and Effective Masses for Charge carriers in an Organic-Inorganic Tri-halide Perovskite
• Determination of the exciton binding energy and effective masses for the methylammonium and formamidinium lead tri-halide perovskite family
• Intrinsic femtosecond charge generation dynamics in a single crystal organometal halide perovskite

Cited by in corpus (7)

• Identification of Free and Bound Exciton States and Their Phase-Dependent Trapping Behavior in Lead Halide Perovskites
• Four-wave mixing in perovskite photovoltaic materials reveals long dephasing times and weaker many-body interactions than GaAs
• Carrier Diffusion in Thin-Film CH3NH3PbI3 Perovskite Measured using Four-Wave Mixing
• Photon echo polarimetry of excitons and biexcitons in a CH${}_3$NH${}_3$PbI${}_3$ perovskite single crystal
• Ultrafast acoustic phonon scattering in CH${}_3$NH${}_3$PbI${}_3$ revealed by femtosecond four-wave mixing
• Free-electron effects on optical absorption of hybrid perovskite CH${}_3$NH${}_3$PbI${}_3$ from first principles
• Long-living dark coherence brought to light by magnetic-field controlled photon echo