Over the last seven years we have witnessed the rise of lead-halide perovskites for optoelectronic applications such as photovoltaics, sensors and light-emitting diodes. In the first part of this talk I will briefly showcase recent efforts towards new materials that are alternatives to traditional lead-halide perovskites, for which computational design approaches from first-principles have been extensively successful and revealed a series of new compounds within the so-called halide double perovskites family [1-3]. All of them exhibit low carrier effective masses and consequently, are prominent candidates for a range of opto-electronic applications such as photovoltaics, light-emitting devices, sensors, and photo-catalysts. I will outline the computational design strategy that lead to the synthesis of these compounds, and particularly focus on the insights we can get from first-principles calculations in order to facilitate the synthesis, improve their opto-electronic properties and the in-silico identification of compounds with properties that are similar to the lead-halide perovskites.
In addition, I will employ a computational design strategy to explore the missing link between halide and oxide perovskites, and demonstrate that for each halide perovskite there are several lookalike oxides with similar optoelectronic properties. Our new concept of analogs led us to identify a new oxide double perovskite semiconductor, Ba2AgIO6, which exhibits an electronic band structure remarkably similar to that of our recently discovered halide double perovskite Cs2AgInCl6, but with a band gap in the visible range at 1.9 eV. [4] I will show results on the successful synthesis of Ba2AgIO6 by solution process and its crystallographic and optical characterization. Ba2AgIO6 and Cs2AgInCl6 are both analogs of the well-known transparent conductor BaSnO3, but the significantly lower band-gap of Ba2AgIO6 makes this new compound much more promising for oxide-based optoelectronics and for novel monolithic halide/oxide devices [4].
In the second part of this talk, I will address the crucial interface of prototype perovskites with two-dimensional materials by means of first-principle calculations. I will show the information we can probe on the atomic-scale mechanisms that underlie charge carrier extraction from the active materials. I will show that there is an interfacial electrostatic dipole that favours electron extraction in the case of graphene – CH3NH3PbI3 interfaces, due to charge re-arrangement, which is formed as soon as the two materials are in contact. Furthermore, we identify a small ferroelectric effect within the first few atomic layers of CH3NH3PbI3 that would also facilitate electron extraction to graphene. In an effort to include the case of partly oxidized graphene and graphene-oxide, which are more relevant materials to technology applications, I will also show effect of oxygen concentration on the electronic level alignment and dipole formation. [5]
In the last part, I will focus on the intrinsic properties of the well-known photovoltaic material FAPbI3. I will show how first-principles calculations can be employed to interpret oscillations that appear on the absorption spectrum of FAPbI3 thin films [6].
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