Spectroscopic Characterisation of Methyl-ammonium Mixed Halide Perovskite Photovoltaic Devices and Microcavities for Optically-Pumped Perovskite Lasers
Felix Deschler a, David-Dominik Jarausch a, Lina Klintberg a, Ruben Higgler a, Sven Huttner a, Michael Price a, Richard Friend a, Henry Snaith b, Sandeep Pathak b
a University of Cambridge - UK, The Old Schools, Trinity Ln, Cambridge CB2 1TN, UK, Cambridge, United Kingdom
b University of Oxford, Clarendon Laboratory, Parks rd, Oxford, 0, United Kingdom
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Poster, Michael Price, 293
Publication date: 1st March 2014

Organometallic mixed halide perovskite- based solar cells have recently shown a breakthrough in power conversion efficiency, with devices exceeding 15 percent12. The high PL efficiency of CH3NH3PbI3-xClx makes it ideally suited to photovoltaic devices, and also to light emitting devices. We show with ultrafast transient absorption and photoluminescence measurements that charge generation in these materials occurs within 1 picosecond, and radiative bimolecular recombination is the dominant decay mechanism above low fluence thresholds3. We look more closely at the transient absorption response of full working devices under different electrical biases, and show that larger fields than initially expected are required to induce a change in photo-excited charge lifetime.

Investigating other applications in light of these findings, we present a detailed study of the transient optical response of a perovskite vertical microcavity structure. The fast cavity ring-down time of the central emission mode compared to the other modes, and the increased line narrowing prove amplified spontaneous emission occurs in the materials above the low threshold of 0.2uJ per pump pulse. Further, intensity correlation measurements with a Hanbury-Brown and Twiss setup show a large decrease in the second order auto-correlation function of emitted light above threshold at zero time delay. This proves coherent light emission and the first instance of an optically pumped perovskite laser. 


Emission spectrum of a vertical microcavity with structure as shown in the inset using a perovskite film as gain medium. The thickness of the perovskite layer was around 500nm and around 1µm for the PMMA layer. Excitation was performed with a pulsed laser (400ps) at 2.33eV and fluences as stated. At low fluences three modes are resonant in the cavity with a mode spacing of ~9.5THz. At sufficiently high fluences the mode at 1.6eV is amplified.
1. Liu, M., Johnston, M. B. & Snaith, H. J. Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature (2013). doi:10.1038/nature12509 2. Burschka, J. et al. Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nature 3–7 (2013). doi:10.1038/nature12340 3. Deschler, F. et al. High Photoluminescence Efficiency and Optically-Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 140324121627005 (2014). doi:10.1021/jz5005285
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