Abhishek Swarnkar1 2 Ashley Marshall2 Kyu Sim3 Erin Sanehira2 Naresh Kumawat4 Dinesh Kabra4 Dae Chung3 Joseph Luther2 Angshuman Nag1

1, Indian Institute of Science Education and Research, Pune, , India
2, National Renewable Energy Laboratory, Golden, Colorado, United States
3, Daegu Gyeongbuk Institute of Science & Technology, Daegu, , Korea (the Republic of)
4, IIT Bombay, Mumbai, IIT Powai, India

I will discuss about a defect-tolerant luminescent nanocrystal (NC), namely colloidal CsPbX3 (X= Br and I) NCs.1 Unlike traditional CdSe based quantum dots (QDs), without any surface modifications, these colloidal NCs have high photoluminescence (PL) quantum yield (QY) (55-90%) with narrow line width (83-153 meV).1,2 Luminescence from films of weakly quantum confined ~11 nm CsPbBr3 NCs does not suffer from the vexing problems of self-absorption and FRET.1 Along with high luminescence, these CsPbBr3 NCs have exceptionally high terahertz (THz) charge carrier mobility of ~4500 cm2V-1S-1 with large diffusion length of > 9.2 µm.3 Ultrafast transient absorption measurement shows exciton binding energies of ~30 meV in CsPbBr3 NCs.4 Based on these advantageous optoelectronic properties, devices employing CsPbX3 NCs (Solar cell, photodiode, LED) have been fabricated.
CsPbI3 is an all-inorganic analogue to the CH3NH3PbI3. However, the cubic phase of bulk CsPbI3 is only stable at high temperature, preventing its adoption within the community. Here, I will describe formation of cubic phase CsPbI3 NC films, phase stability for months in ambient air, with long-range electronic transport, leading to the fabrication of the first colloidal perovskite NC solar cells with a Voc= 1.23 V and PEC = 10.77 %.2 These devices also exhibit electroluminescence with low turn-on voltage and tunable emission. We also have made stable and hysteresis-free photodiode of high detectivity (1.8 x 1012 Jones) and reliability using CsPbI3 NCs as photoactive material.5 Eventually, following the same film fabrication method and to use high PLQY of CsPbBr3, we have made LED exhibiting ~ 6 cd/A luminance efficiency and 2.25% external quantum efficiency (EQE) with a device structure of ITO/PEDOT:PSS/CsPbBr3-QDs/TPBi/Ca/Ag.6 The synthesis of normally non-luminescent and unstable material phases stabilized through colloidal NC synthesis provides another mechanism for materials design for other applications. All these optoelectronic behaviors of CsPbX3 perovskite NCs are advantageous, and therefore, CsPbX3 NC can be a better candidate for optoelectronics.

1. Swarnkar, A.; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag, A. Angew. Chem., Int. Ed.2015, 54, 15424
2. Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, D. T.; Christians, J. A.; Chakrabarti, T.; Luther, J. M. Science 2016, 354, 92.
3. G. R. Yettapu, D. Talukdar, S. Sarkar, A. Swarnkar, A. Nag*, P. Ghosh*, P. Mandal*,Nano Letters, 2016, 16, 4838
4. J. Aneesh, A. Swarnkar, V. K. Ravi, R. Sharma, A. Nag*, K. V. Adarsh*. J. Phys. Chem. C, 2017, 121, 4734
5. Sim, K.M.; Swarnkar, A.; Nag, A.; Chung, D.S. Laser Photonics Rev. 2017, 1700209.
6. Data Unpublished