Understanding Excited State Behavior as the Key to Evaluate the Photovoltaic Performance of Perovskite Materials

Prashant Kamat^a^,^c, Joseph Manser^a^,^c, Jeffrey Christians^a^,^c

^aUniversity of Notre Dame, US, Notre Dame, Indiana 46556, EE. UU., Notre Dame, United States

^bUniversity of Notre Dame, US, Notre Dame, Indiana 46556, EE. UU., Notre Dame, United States

^cUniversity of Notre Dame, US, Notre Dame, Indiana 46556, EE. UU., Notre Dame, United States

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Invited Speaker, Prashant Kamat, presentation 307
Publication date: 5th February 2015

Photoinduced charge separation in light harvesting materials is the primary step in light energy conversion devices. Both time-resolved absorption and emission spectroscopy have served as the important tool in the characterization of excited behavior of quantum dots in quantum dot solar cells [1]. With the emergence of highly efficient perovskite materials, there is a need to understand the excited state behavior and charge separation events in these new materials. The scientific issue related to the understanding of the excited state behavior of organic metal halide perovskite materials remains a scientific challenge. Photoexcitation of perovskite film leads to efficient charge separation and the fate of charge carriers is determined by the bimolecular recombination rate [2]. Transient absorption spectroscopy measurements have now revealed the existence of a charge transfer state in addition to the charge separated state [3]. The interaction of CH₃NH₃PbI₃ with water vapor (90% humidity exposure) has allowed us to identify the transformations leading to the deterioration of the perovskite solar cells. While significant changes are seen in the UV-visible absorbance, the presence of the hydrate in the films has no noticeable effect on the charge carrier dynamics at short times (< 1.5 ns). It is proposed that H₂O initially reacts with the surface of the perovskite film, and only slowly permeates through to the center of large domains. The reaction with H₂O at the surface of the perovskite film forms shallow traps in the band structure so that the portion of the CH₃NH₃PbI₃ crystal which is pristine remains largely unaffected. The results related to size dependent photovoltaic performance of excited state behavior of CH₃NH₃PbI₃ films will also be discussed [4, 5].

[1] Kamat, P. V. Quantum Dot Solar Cells. The Next Big Thing in Photovoltaics, J. Phys. Chem. Lett., 2013, 4, 908-918 [2] Manser, J. S.; Kamat, P. V., Band Filling with Charge Carriers in Organometal Halide Perovskites. Nature Photonics 2014, 8, 737-743. [3] Stamplecoskie, K. G.; Manser, J. S.; Kamat, P. V. Dual Nature of the Excited State in Organic-Inorganic Lead Halide Perovskites Energy Environ. Sci. 2015, 8, 208-215 [4] Chen, Y.-S.; Manser, J. S.; Kamat, P. V., All Solution-Processed Lead Halide Perovskite-BiVO4 Tandem Assembly for Photolytic Solar Fuels Production. J. Am. Chem. Soc., 2015, 137, 974-981. [5] Christians, J. A.; Miranda Herrera, P. A.; Kamat, P. V., Transformation of the Excited State and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite upon Controlled Exposure to Humidified Air. J. Am. Chem. Soc. 2015, DOI: 10.1021/ja511132a

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