Organic-inorganic hybrid Perovskites: from photophysical properties to optoelectronic

Abstract

Hybrid perovskites are one of the most promising materials for low-cost and high-efficiency photovoltaic technologies. However, the understanding of their physical properties has lagged behind the impressive improvement of power-conversion efficiency (>20%). In the first part of my presentation I will report about the optical properties of FAPbI3 perovskite films based on different precursor systems (the formamidinium iodide (FAI)/HPbI3, FAI/PbI2, and FAI/PbI2 with HI additive). Exciton binding energies of 8.1 meV for the high temperature phase and 18 meV for the low temperature phase are extracted. At room temperature, we found the lifetimes to vary from tens to hundreds nanoseconds. FAPbI3 film made from the new precursor, exhibits the longest lifetime of 439 ns, suggesting a lower number of defects and lower non-radiative recombination losses compared with FAPbI3 obtained with the other two precursors set. From the low temperature data we estimated the exciton-optical phononcoupling coefficient to be about 35 meV, and the optical phonon energy 18 meV. This latter value is assumed to be the effective average, since the FAPbI3 lattice possesses more than one optical phonon.

I will conclude my presentation, discussing the importance of the surface recombination in hybrid perovskite based solar cells. By tuning the nature of electron extracting layer, efficiency above 16% and suppression of the so-called light soaking effect, are obtain in flat device structures. The light soaking effect is one of the causes of instability of the power output of perovskite solar cells, therefore is extremely important to understand its origin and supress it to make of hybrid perovskite optoelectronic devices a viable technology.