Functionalization of transparent conductive oxide electrode for TiO2-free perovskite solar cells

Many of the best performing solar cells based on perovskite-halide light absorbers use TiO2 as an electron selective contact layer. However, TiO2 usually requires high temperature sintering, is related to electrical instabilities in perovskite solar cells, and causes cell performance degradation under full solar spectrum illumination. Here we demonstrate an alternative approach based on the modification of transparent conductive oxide electrodes with self-assembled siloxane-functionalized fullerene molecules, eliminating TiO2 or any other additional electron transporting layer. We demonstrate that these molecules spontaneously form a homogenous monolayer acting as an electron selective layer on top of the fluorine doped tin oxide (FTO) electrode, minimizing material consumption. We find that the fullerene-modified FTO is a robust, chemically inert charge selective contact for perovskite based solar cells, which can reach 15% of stabilised power conversion efficiency in a flat junction device architecture using a scalable, low temperature, and reliable process. In contrast to TiO2, devices employing a molecularly thin functionalized fullerene layer show unaffected performance after 67 h of UV light exposure

Interfacial Morphology Addresses Performance of Perovskite Solar Cells Based on Composite Hole Transporting Materials of Functionalized Reduced Graphene Oxide and P3HT

The development of novel hole transporting materials (HTMs) for perovskite solar cells (PSCs) that can enhance device's reproducibility is a largely pursued goal, even to the detriment of a very high efficiency, since it paves the way to an effective industrialization of this technology. In this work, we study the covalent functionalization of reduced graphene oxide (RGO) flakes with different organic functional groups with the aim of increasing the stability and homogeneity of their dispersion within a poly(3-hexylthiophene) (P3HT) HTM. The selected functional groups are indeed those recalling the two characteristic moieties present in P3HT, i.e., the thienyl and alkyl residues. After preparation and characterization of a number of functionalized RGO@P3HT blends, we test the two containing the highest percentage of dispersed RGO as HTMs in PSCs and compare their performance with that of pristine P3HT and of the standard Spiro-OMeTAD HTM. Results reveal the big influence of the morphology adopted by the single RGO flakes contained in the composite HTM in driving the final device performance and allow to distinguish one of these blends as a promising material for the fabrication of highly reproducible PSCs

Characterization of Radiation Hardness of Organic Transistors for a Flexible X-Ray Imager

We present the characterization of complementary p-type and n-type organic transistors in terms of X-ray radiation hardness. These transistors are fabricated as the backplane of an array of photo-conductive pixels based on perovskites for direct X-ray imaging on flexible substrates. Experimental results show that irradiation up to 1 kGy produces negligible effects (a tolerable maximum shift of the transistor threshold voltage of about 40% right after exposure, which is almost completely recovered after 24 hours at rest)

Development of a Flexible X-Ray Imager Based on Metal Halide Perovskites

This work presents the design and preliminary characterization of flexible X-ray imager for large-area tomographic applications. Each pixel consists of methylammonium lead tri-iodide (MAPbI 3 ) perovskite particles, acting as photoconductor deposited on top of interdigitated microelectrodes. Pixels are organized in arrays and individually addressed by commercial OFETs fabricated on a plastic backplane acting as matrix substrate. A demonstrator array of 4 by 4 pixels of 1 mm side is here presented. We report on the characterization of the detectable response to X-ray irradiation (up to 40 kV tube voltage) of the pixel on a glass substrate, the successful radiation hardness of the backplane OFETs (up to 1 kGy received dose) and a preliminary characterization of the bendable array fabricated on plastic

Functionalization of transparent conductive oxide electrode for TiO2-free perovskite solar cells

Many of the best performing solar cells based on perovskite-halide light absorbers use TiO2 as an electron selective contact layer. However, TiO2 usually requires high temperature sintering, is related to electrical instabilities in perovskite solar cells, and causes cell performance degradation under full solar spectrum illumination. Here we demonstrate an alternative approach based on the modification of transparent conductive oxide electrodes with self-assembled siloxane-functionalized fullerene molecules, eliminating TiO2 or any other additional electron transporting layer. We demonstrate that these molecules spontaneously form a homogenous monolayer acting as an electron selective layer on top of the fluorine doped tin oxide (FTO) electrode, minimizing material consumption. We find that the fullerene-modified FTO is a robust, chemically inert charge selective contact for perovskite based solar cells, which can reach 15% of stabilised power conversion efficiency in a flat junction device architecture using a scalable, low temperature, and reliable process. In contrast to TiO2, devices employing a molecularly thin functionalized fullerene layer show unaffected performance after 67 h of UV light exposure

Humidity-robust scalable metal halide perovskite film deposition for photovoltaic applications

Organic-inorganic perovskite photovoltaics have now achieved power conversion efficiencies at par with silicon devices on a lab-scale. To enable industrial application of the technology, developing a perovskite deposition route compatible with scalable, large-area deposition methods, which exploits safer processing solvents and is robust to variations of the processing parameters, particularly humidity, is highly demanded. To satisfy such constraints altogether, here we introduce a lead iodide-hydroiodic acid-water precursor (PbI2-HI-H2O) that enables the scalable deposition of methylammonium lead triiodide (MAPbI3) films from a safer solvent (acetonitrile-ACN) in a wide range of high moisture levels, spanning from 50 to 80% relative humidity. When exposed to a methylamine (MA) gas flow the PbI2-HI-H2O precursor readily converts to specular perovskite films. If heated, the PbI2-HI-H2O film can be easily reverted to PbI2, further enabling the implementation of two step deposition methods. Our process was tested in an inverted solar cell configuration achieving stabilized power conversion efficiencies of 14% with minimal annealing requirements. Our findings demonstrate an appealing route for a large-area compatible manufacturing of hybrid perovskite photovoltaics in air, at high moisture levels, based on solvents of reduced hazard