Anomalous increase of the photoluminescence decay time with the temperature in CsPbBr3 nanocrystals: role of the thermally activated transfer from the surface states

Fabio Gabelloni^a, Giulia Andreotti^a, Francesco Biccari^a, Massimo Gurioli^a, Marco Pagliai^b, Alessio Milanesi^b, Nicola Calisi^b, Stefano Caporali^c, Anna Vinattieri^a

^aDepartment of Physics and Astronomy, University of Florence and LENS, via G. Sansone 1, Sesto Fiorentino (FI), Italy

^bDepartment of Chemestry, University of Florence, via della Lastruccia 3, Sesto Fiorentino (FI), Italy

^cDepartment of Industrial Engineering , University of Florence, via di S.Marta 3, Firenze, Italy

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2017 (NFM17)

SE1: Fundamental Processes in Semiconductor Nanocrystals

Barcelona, Spain, 2017 September 4th - 9th

Organizers: Arjan Houtepen and Zeger Hens

Poster, Fabio Gabelloni, 158
Publication date: 20th June 2016

Metal halide perovskites represent a very promising alternative to hybrid organic perovskites, given their better long-term stability and impressive radiative yield. Therefore such materials are extremely attracting not only for tandem photovoltaic cells but also for manufacturing efficient LEDs and lasers allowing to cover a spectral range from NUV to NIR depending on the halide composition. Despite the large amount of reports on inorganic perovskites in the last few years, systematic studies concerning the carrier recombination dynamics are missing and very little is known concerning the role of surface states in ruling the electron-hole / exciton recombination.

In this contribution, we present continuous-wave (CW) and picosecond time-resolved (TR) photoluminescence (PL) results on drop-cast CsPbBr₃ nanocrystals from 10 K to 300 K. Several PL band from different size nanocrystals are detected and related to quantum confinement effects. PL spectra show spectral broadening of the order of 20 meV, thus indicating the high material quality. This result is also confirmed by power dependent measurements, which bring evidence of the excitonic nature of the recombination. Non -exponential PL decays are observed in agreement with literature results. In particular, fitting with a two-exponential curve and taking into account the excitation laser pulse repetition rate, we report the dependence of the first decay constant on the PL band energy, which suggests a close relation with the carrier confinement. Raising the temperature, a significant increase of the PL decay time is reported, indicating the thermal activation of a transfer process from non-radiative states. This phenomenon, which is resulted dependent on both the nature of the chemical precursors used and the morphology of the deposited crystals, presents a close correlation with the emission energy and could be ascribed to surface states. By a careful analysis of the PL decays as a function of temperature, we determined the activation energy for the different PL bands. It turns out to be of the order of 26 meV for micro-size crystals and roughly a factor two smaller for sub-micron size ones.

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