Center for Integration of Modern Optoelectronic Materials on Demand (IMOD)

Perovskites and Hybrid Structures: We will focus on developing 3D, 2D and 0D halide perovskites which represent a key class of semiconductors that can be processed from solution with exceptional optoelectronic quality high defect tolerance, coherent emission, and potentially unique photocarrier dynamics attributed to large polaron physics. These compounds offer facile tunability in their own right, and are promising matrices for incorporation of well-passivated mixed-dimensionality quantum structures, in both all-perovskite, and perovskite/non-perovskite forms. In the case of 2D perovskites will optimize the strong excitonic confinement which leads to exciton binding energies as low as 40 and as high as 500 meV. We choose the 2D perovskites because they offer a versatile platform for manipulating light through synthetic design, and for tailoring Coulomb interactions on different timescales with dipolar and/or polarizable organic cations. We will optimize the emission from 2D perovskites which covers a broad region of the electromagnetic spectrum and can be very color pure or extremely broad depending on the operative luminescence mechanism. We will examine synthetic control of layer thickness (n) as the primary predictor of OE properties, in particular bright light emission with controllable linewidth. We will systematically control of platelet thickness and dielectric confinement, varying both the inorganic, and organic components, which will lead to greater quantum yields and higher stability. Another synthetic challenge is how to target either narrow (excitonic) or broadband (self-trapped) emission as desired. We will investigate how the tuning the of the local structural distortions in n=3 mixed bromide/chloride (ethylammonium)4Pb3Br10-xClx solid solution perovskites can control the light emission properties and emission line width. We will use carefully selected members of the library of 2D perovskites of the type (Spacer cation)2(MA)n−1PbnI3n+1 (n = 1–7) contains members because they are exceptionally stable to the ambient and also under light soaking for certain spacer cations for over 500 days. We will measuring the Young’s modulus and hardness of these 2D perovskites and study how increasing the side carbon chain length of spacer molecules, one can adjust the softness of the material, since will have positive implications in the use of these semiconductors in flexible substrates. We will also study the local, static structural distortions in semiconductors resulting from halide mixing, such as (ethylammonium)4Pb3Br10-xClx solid solution perovskites, or extrinsic doping, as for lanthanide doping of hybrid NC-perovskites. These will have a strong impact on emission properties (e.g., narrow vs broadband), but can be challenging to characterize. To quantify the local structural distortions in 2D solid solution perovskite single crystals, we will use neutron and X-ray diffuse scattering as well as pair distribution function measurements. The local environment around the lanthanide dopants with be probed with XAS. These methodologies will be aided by insight from computation within IMOD and complemented by TEM, although this is challenging with soft perovskites.