Pb-halide perovskites exhibit defect-tolerant behaviour resulting into efficient optoelectronic properties. We have worked on various aspects of material design, optical and optoelectronic properties of colloidal cesium lead halide perovskite nanocrystals.^1-5 The key aspects that make Pb-halides an unique class of optoelectronic materials are: (i) Pb²⁺ exhibit stable nS² electronic configuration in the outermost orbital, (ii) small effective masses of charge carriers because of 3-D structural network of [PbBr₆]^4- octahedra with Pb-Br-Pb bond angles close 180^o, and (iii) strong spin-orbit splitting of Pb 6p states (conduction band minimum).

From last couple of years, we have started searching for colloidal Pb-free metal halide nanocrystals that can exhibit the combination of these three properties.^6-7 In this talk, I will discuss about our experiences on Pb-free metal halide nanocrystals. The Pb-free materials that will be discussed are colloidal thallium halide (TlX), cesium antimony halide (M₃Sb₂X₉; M = Cs and Rb), and cesium bismuth halide (Cs₃Bi₂X₉) nanocrystals, where X signifies halides. Intrinsic issues regarding material design and photophysical properties relevant for optoelectronic applications will be discussed.

References:

1. Swarnkar, A; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag A. Angew. Chem. Int. Ed. 2015, 53, 15424.

2. Yettapu, G. R.; Talukdar, D.; Sarkar, S.; Swarnkar, A.; Nag, A.; Ghosh, P.; Mandal, P. Nano Lett. 2016, 16, 4838.

3. Ravi, V. K.; Markad, G. B.; Nag, A. ACS Energy Lett.2016, 1, 665.

4. Mir, W. J.; Jagadeeswarara, M.; Das, S.; Nag, A. ACS Energy Lett., 2017, 2, 537.

5. Sarkar, S.; Ravi, V. K.; Banerjee, S.; Yettapu, G. R.; Markad, G. B.; Nag, A.; Mandal, P. Nano Lett., 2017, 16, 5402.

6. Swarnkar, A.; Ravi, V. K.; Nag, A. ACS Energy Lett., 2017, 2, 1089.

7. Mir, W. J; A. Warankar, A.; Acharya, A.; Mandal, P.; Nag, A. Chem. Sci. 2017, 8, 4602.

8. Pal, J.; Manna, S.; Mondal, A.; Das, S.; Adarsh, K. V.; Nag, A. Angew. Chem. Int. Ed. 2017, 56, 14187.