Direct Observation of Ultrafast Exciton Dissociation in Lead Iodide Perovskite by 2D Electronic Spectroscopy

作者：Jha Ajay; Duan Hong Guang; Tiwari Vandana; Nayak Pabitra K; Snaith Henry J; Thorwart Michael; Miller R J Dwayne

来源：ACS Photonics, 2018, 5(3): 852-860.

DOI：10.1021/acsphotonics.7b01025

• photovoltaics
• Wannier exciton
• binding energy
• exciton-phonon coupling
• electronic dephasing
• vibrational modes

The unprecedented success of hybrid organic-inorganic lead halide perovskites in photovoltaics motivates fundamental research to unravel the underlying microscopic mechanism for photoinduced charge generation. Recent studies suggest that most photoexcitations in perovskites are free charge carriers, although the contribution of the electron-hole pairs (i.e., excitons) at room temperature has been a matter of debate. We have employed ultrafast two-dimensional (2D) electronic spectroscopy to directly probe the elementary optical excitation of CH3NH3PbI3 thin films with similar to 16 fs temporal resolution. We distinctly capture the ultrafast dissociation of excitons to the charge carriers at room temperature and at 180 K. Interestingly, we also observe that the coherent oscillations of the off-diagonal signals in the 2D electronic spectra live for similar to 50 fs at room temperature. The entropy-driven dissociation of excitons to charge carriers happens within the electronic dephasing time scale and is favored by the low exciton binding energy, which we determine to be similar to 12 meV at room temperature. This ultrafast dissociation of excitons to charge carriers can be one of the important contributions to the high efficiency of perovskite-based photovoltaics.

• 出版日期2018-3