4:15 PM - CP02.08.04
Colloidal Cs1-xFAxPbI3 Perovskite Nanocrystals with Full Range of A-Site Composition Tuning for High VOC Solar Cells
Joseph Luther1,Abhijit Hazarika1,Qian Zhao1,2,Ashley Gaulding1,Jeffrey Christian1,Benjia Dou1,3,Ashley Marshall1,Taylor Moot1,Joseph Berry1,Justin Johnson1
National Renewable Energy Laboratory1,Nankai University2,University of Colorado Boulder3
Due to their amazing optoelectronic properties, colloidal lead halide perovskite nanocrystals (NCs) are receiving increasing attention in recent times.1,2 Perovskite NCs possess properties that are not accessible in their bulk or thin-film counterparts. For example, perovskite phase of CsPbI3 is unstable in ambient condition in bulk or thin-film, but they are phase stable in their quantum confined form. This particular material has shown to have record efficiency for quantum dot (QD) solar cells.3,4 Another interesting advantage of these QD materials is that their compositions can be tuned without changing the crystal framework either by direct synthesis or by post-synthetic ion exchanges. Particularly, X-site ion exchange in the perovskite QDs with general formula ABX3 (where A= Cesium-Cs, methylammonium-MA, formamidinium-FA etc.; B= Pb or Sn; X= Cl, Br, I) has shown to be very facile.5 On the other hand, A-site composition tunability is very limited in these materials, or even in the corresponding thin films. For example, it is known that any arbitrary composition in Cs1-xFAxPbI3 cannot be achieved both in QDs and thin films, and it has been shown that only compositions with 1-x>0.4 can be realized in the pure usable perovskite phase. This is due to thermal instability of FAPbI3 (crystallizes at around 130 oC) at temperatures required to crystallize CsPbI3 (above 300 oC). Here, we present a simple post synthetic cross-cation exchange reaction between colloidal solutions of CsPbI3 and FAPbI3 nanocrystals just by mixing them at temperatures slightly above the room temperature that enables us to achieve compositions in the whole range of 0<x<1. This helps us to realize compositions that were not known previously. The photoluminescence (PL) kinetics studies reveal that the activation energy required to inter-exchange the Cs+ and FA+ ions is around 0.65 eV, higher than that for X-site exchange in lead halide perovskites. We use these alloyed colloidal perovskite quantum dots to fabricate photovoltaic devices. We applied these alloyed NC ink in solar cell and demonstrated that they exhibited high open circuit voltage (VOC) of ~ 90% of their Shockley-Quiesser maximium and have lower losses than the thin film perovskite devices of similar compositions.6
1. Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V., Nano Lett. 2015, 15 (6), 3692.
2. Akkerman, Q. A.; Rainò, G.; Kovalenko, M. V.; Manna, L., Nat. Mater. 2018, 17 (5), 394.
3. 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 (6308), 92.
4. Sanehira, E. M.; Marshall, A. R.; Christians, J. A.; Harvey, S. P.; Ciesielski, P. N.; Wheeler, L. M.; Schulz, P.; Lin, L. Y.; Beard, M. C.; Luther, J. M., Sci. Adv. 2017, 3 (10).
5. Akkerman, Q. A.; D’Innocenzo, V.; Accornero, S.; Scarpellini, A.; Petrozza, A.; Prato, M.; Manna, L., J. Am. Chem. Soc. 2015, 137 (32), 10276.
6. Abhijit Hazarika, Qian Zhao, E. Ashley Gauldin, Jeffrey A. Christians, Benjia Dou, Ashley R. Marshall, Taylor Moot, Joseph J. Berry, Justin C. Johnson, and Joseph M. Luther, ACS Nano, 2018, 12 (10), 10327.