Bimodal Porosity and Stability of a TiO2 Gig-Lox Sponge Infiltrated with Methyl-Ammonium Lead Iodide Perovskite.

Salvatore Sanzaro,Corrado Spinella,Corrado Bongiorno,Fortunato Neri,Emanuele Smecca,Giovanni Mannino,Federico Zontone,Antonino La Magna,Alessandra Alberti,Thomas Bottein,David Grosso

doi:10.3390/nano9091300

Abstract

We created a blend between a TiO2 sponge with bimodal porosity and a Methyl-Ammonium Lead Iodide (MAPbI3) perovskite. The interpenetration of the two materials is effective thanks to the peculiar sponge structure. During the early stages of the growth of the TiO2 sponge, the formation of 5–10 nm-large TiO2 auto-seeds is observed which set the micro-porosity (<5 nm) of the layer, maintained during further growth. In a second stage, the auto-seeds aggregate into hundreds-of-nm-large meso-structures by their mutual shadowing of the grazing Ti flux for local oxidation. This process generates meso-pores (10–100 nm) treading across the growing layer, as accessed by tomographic synchrotron radiation coherent X-ray imaging and environmental ellipsometric porosimetry. The distributions of pore size are extracted before (>47% V) and after MAPbI3 loading, and after blend ageing, unfolding a starting pore filling above 80% in volume. The degradation of the perovskite in the blend follows a standard path towards PbI2 accompanied by the concomitant release of volatile species, with an activation energy of 0.87 eV under humid air. The use of dry nitrogen as environmental condition has a positive impact in increasing this energy by ~0.1 eV that extends the half-life of the material to 7 months under continuous operation at 60 °C.

Highlights

We demonstrate that our gig-lox TiO2 scaffold blended with MAPbI3 has a high stability and durability, and that the degradation process is mostly related to the eventual presence of an adverse environment rather than to the multiple interfaces established inside the blend
Tomographic X-ray imaging (CXDI) acquired with synchrotron radiation on fragments of samples revealed a meso-porosity in the range ~10–100 nm that was subsequently exploited for perovskite loading
coherent synchrotron X-ray-based diffraction imaging (CXDI) 3D-Imaging depicted a scenario of large perovskite infiltration along the meso-pores by mapping the electronic density distribution per unit volume into fragments of the blend, with pore filling estimated above 80% in volume

Summary

Introduction

Titanium dioxide (TiO2), since the discovery of its application to water photolysis by Fujishima and Honda in 1972 [1], has progressively raised interest in many different fields such as for photocatalytic degradation of pollutants [2,3,4], photocatalytic CO2 reduction into energy fuels [5,6,7,8], water splitting [9,10,11], solar cells and photonics [12,13], sensors [14,15,16], supercapacitors [17,18], biomedical devices [19,20,21] and lithium-ion batteries [22,23,24].In the photovoltaic field, recent advances were linked to the application of porous TiO2 in hybrid solar cell architecture with efficiency that went up strikingly rapidly [25] thanks to the new ideas of M. Since perovskite are required to form an interconnected blend with its scaffold, issues related to the accessibility of the TiO2 pores, effectiveness of the perovskite reaction [39,40], and the stability and durability of the blend [41,42,43,44,45,46,47,48,49,50,51,52,53] need to be faced In this respect, the pore filling capability is a parameter of high technological impact [54]

Methods

Results

Conclusion