Juan P. Martínez-Pastor
Instituto de Ciencia de Materiales, Universidad de Valencia (ICMUV), Catedrático José Beltrán 2, 46980 Paterna, Spain

The continuous development in smart devices and microsystems for the control of industrial processes, biomedical sensors and instruments, visible and NIR light communications, as many other applications, is triggering new demands for photonic chips. Metal halide perovskites (MHPs) can be a good solution, because of their good optoelectronic properties and tolerance against crystalline defects, other than low-cost processing and low CO₂ footprint. In the present talk the optical properties of several 2D MHPs of formula ABX₃ (A = organic cation, B = Pb, Sn, X = I) have been investigated and will be presented in this talk.
First of all, basic optical properties of Pb-perovskites, as PEA₂PbI₄ (and higher order Ruddlesden-Popper phases), will be presented, both in the case of polycrystalline thin films and nanoflakes with lateral size greater than 10 µm. Moreover, these nanoflakes can be the base of micrometric photodevices by using Pt-prepatterned Si/SiO₂ substrates with channel lengths in the range 2-10 µm. Measured photocurrent is highly dependent on the thickness flake due to the great absorption coefficient and negligible carrier transport in the vertical direction. Interestingly, in the case of few layer nanoflakes, photocurrents from 10 pA to 100 nA can be measured in the range 10 pW to more than 500 nW.
Sn-perovskites are also very interesting 2D semiconductors, because they are non-toxic alternatives of Pb-perovskites for applications as photodevices. However, the use of Sn-perovskites still suffers from very low stability and most of the synthesis, fabrication and/or characterization work must be done under inert atmosphere or vacuum, even if antioxidative synthetic routes can be followed for reducing the negative effect of ambient conditions. 2D tin-perovskites, TEA₂SnI₄, are gaining more stability and resistance to ambient condition, whose deposition is possible by scalable solution processing techniques as Inkjet-printing. Room- and low-temperature excitonic PL and charge carrier recombination dynamics in (TEA)₂SnI₄ thin films were studied and demonstrated two excitonic optical transitions. The analysis of micro-PL measurements suggests that the low-energy emission line is associated to the volume of perovskite grains (platelets), while the high-energy excitonic transition seems to be originated at the platelet edges (as identified in the biggest ones). Photoconductive detectors based on TEA₂SnI₄ inkjet-printed films were also studied after encapsulation. High electrical (dark currents as low as ~ 10 – 20 nA at 10 V of bias voltage) and electro-optical parameters (responsivities in the range 1-20 A/W) were obtained for these photodevices under ambient conditions over several weeks.