(604e) Discovery of Near-Infrared-Active Colloidal Multinary Lead Halide Perovskite Nanocrystals Using a Microfluidic Platform 

Authors: 
Lignos, I., Massachusetts Institute of Technology
Morad, V., ETH Zürich
Maceiczyk, R., ETH Zürich
Protesescu, L., ETH Zürich
Kovalenko, M. V., ETH Zurich
deMello, A. J., ETH Zurich
Lead-based metal halide perovskites, APbX3 structures, with organic-inorganic A-site cations (A = methylammonium (MA) CH3NH3+, formamidinium (FA), CH3(NH2)2+, Cs, Rb) and an anion (X = Cl, Br, I) have opened exciting opportunities in the perovskite-based solar cell devices with unprecedented efficiencies which reach up to 22 %.1 However, red and near infrared regions still present a challenge for perovskite materials: all three archetypical A-site monocationic perovskites – CH3NH3PbI3, FAPbI3 and CsPbI3 – suffer from either chemical or thermodynamic instabilities. A promising avenue towards mitigation of these challenges lies in the formation of multinary compositions.2 Recently, lead based perovskites with mixed-cations on the A site have shown great potential for the fabrication of thermally stable perovskite solar cells with high photoelectric conversion efficiencies.3 In particular, the addition of Cs to FA-based perovskites generally influence the stability and optoelectronic properties of their pure perovskite counterparts.4 The intrinsic challenge in the synthesis of mixed-cation and mixed- halide NCs is to identify the effect of various reaction parameters such as precursor ratios, ligand concentrations, temperature and reaction time on optical and structural characteristics. Recently, we demonstrated the use of microfluidic reactors for the rapid parametric screening and on-line characterization of the optical characteristics of cesium lead halide perovskite NCs while identifying the optimum reaction parameters for their synthesis.5

Herein, we demonstrate for the first time the formation of stable CsxFA1-xPb(Br1-yIy)3 NCs with a concurrent band gap tuning between 690 and 775 nm while presenting the underlying reaction mechanisms using a fully automated droplet-based microfluidic platform. The synthesized Cs/FA perovskite compounds with narrow emission linewidths (45 – 65 nm) overcome the instability issues facing CsPbX3 and FAPbX3 NCs, exhibiting finely stable emission and absorption spectra over long term storage (several weeks). The combination of online photoluminescence and absorption measurements allows for identifying compositional and size effects on the optical properties of the synthesized NCs. Last, the reactions can be directly transferable in conventional laboratory reactors for the large-scale synthesis of CsxFA1-xPb(Br1-yIy)3NCs positioning them as strong candidates for the fabrication of solar cells.

  1. NREL Chart. http://www.nrel.gov/pv/assets/images/efficiency_chart.jpg (05.01.2017),

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  5. Lignos, I.; Stavrakis, S.; Nedelcu, G.; Protesescu, L.; Demello, A. J.; Kovalenko, M. V. Nano Lett. 2016, 16, 1869-1877.