Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.103
Publication date: 6th July 2018
The excellent optoelectronic properties of perovskite nanocrystals (NCs) such as enhanced photoluminescence quantum yield (PLQY) and tunable emission wavelength has stimulated a widespread investigation of this class of semiconductors.[1] Very recently, it has been demonstrated that CsPbBr3 NCs can reach near-unity PLQY in solution. Yet, retaining the PLQY in film is not trivial; since the NCs are not as well passivated as in solution and close packing can lead to energy-transfer to trap-states and increased self-absorption.
Here, a room temperature synthesis of perovskite NCs displaying near-unity PLQY in solid state films is presented.[2] Spin-coated films of the obtained CsPbBr3 NCs show PLQY values approaching unity (>95%), thanks to the combination of a novel synthesis at room temperature, and a post synthetic treatment. The as-obtained NCs show PLQY = 80% in spin-coated films. Further enhancement of the PL efficiency is obtained via addition of PbBr2. Following the synthesis, the obtained NCs were employed in optoelectronic devices. Efficient solar cells based on mixed-halide (CsPbBrI2) NCs obtained via anion exchange reactions under ambient conditions were fabricated.[3]. Solar cell devices operating in the wavelength range 350−660 nm were fabricated in air with two different deposition methods: single step (SP) and layer-by-layer (LbL). The solar cells display a photoconversion efficiency of 5.3%, independently of the active-layer fabrication method, and open circuit voltage (Voc) up to 1.31 V, among the highest reported for perovskite-based solar cells with bandgap below 2 eV, clearly demonstrating the potential of this material.
The high potential of the material is further tested in light-emitting diodes (LEDs) employing an inverted structure comprising of ZnO nanoparticles as an electron-transport layer and a conjugated polymer hole-transport layer. The LEDs demonstrate an external-quantum-efficiency of 6.04%, with luminance of 12998 Cd/m2 and low efficiency droop (around 10%). Importantly, such high efficiency was achieved by substituting Cesium with Formamidinium in line with our synthetic procedure. These results show the versatility of our synthetic protocol while the material quality is pointed out by the high performance of the optoelectronic devices.
References
[1] L. Protesescu, S. Yakunin, M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A. Walsh, M. V Kovalenko, Nano Lett. 2015, 15, 3692.
[2] F. Di Stasio, S. Christodoulou, N. Huo, G. Konstantatos, Chem. Mater. 2017, 29, 7663.
[3] S. Christodoulou, F. Di Stasio, S. Pradhan, A. Stavrinadis, G. Konstantatos, J. Phys. Chem. C 2018, 122, 7621-7626.
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