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Titanium Oxide Nanocomposites for Scalable Optimized Perovskite Solar cells

Periodic Reporting for period 1 - TONSOPS (Titanium Oxide Nanocomposites for Scalable Optimized Perovskite Solar cells)

Reporting period: 2016-03-16 to 2018-03-15

"The application of functional nanostructured materials in industrial processes and advanced science is of capital and strategic importance for the European economy and society. Their inclusion as reliable, standard and affordable components will boost the competitiveness of European industry, specifically in the fabrication of 4th generation solar cells. Sensitized perovskites solar cells represent advantages in terms of cost manufacturing, energy generation and integration in flexible and semitransparent devices. However, the viability of their mass scale fabrication is hindered by economic and technical difficulties. Some of these technical issues arise from inefficient infiltration of the perovskite absorber into a fragile mesoporous TiO2 layer.
""Titanium Oxide Nanocomposites for Scalable Optimized Perovskite Solar cells"" (TONSOPS) project addresses these problems applying a recently developed straightforward method for securing TiO2 nanotube layers to commodity thermoplastic polymers. This novel method combined with optimized solution synthesized perovskites will result in the production of flexible and pliable Perovskites Solar Cells (Figure 1). Specifically, the project proposes to produce a step change in the standardization and fabrication of functional nanostructured materials, and its implementation in optimized solar cells. Lastly, the study on the life cycle management and viability of the industrial production of these Perovskite Solar Cells will be evaluated in an innovative photovoltaic manufacture company, ONYX SOLAR. Hence, the project is designed to generate disruptive, but easily scalable technology that may be rapidly adopted by European industry to boost its competitiveness in functional nanostructured composites and 4th generation solar cells.
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1.-The implantation of nanocomposites fabrication set-up and protocols at “Instituto de Microelectrónica de Madrid”(CSIC) for the synthesis of optimized TiO2 Nanotube Layers/Thermoplastic nanocomposites. The included activities were:
i) New set-up (hardware and software) for the anodic synthesis of TiO2 nanotube layers.
ii) Optimization of the galvanostatic and potentiostatic anodization processes for the production of TiO2 nanotube layers. We have tested several electrochemical conditions to obtain a high control of the aspect ratio (diameter/length) and the three dimensional (3D) modulated nanostructure of the TiO2 nanotubes.
iii) Optimization of different thermal annealing conditions of the TiO2 nanotube layers.
iv) Synthesis of optimized TiO2 nanotube layers / Thermoplastic nanocomposites. We have synthesized series nanocomposties varying the TiO2 nanotubes nanostructure (aspect ratio and 3D modulation) and thermal annealing, combined with common industrial grade thermoplastics (PET, Polycarbonate, PMMA and Polypropylene). Best results, in terms of mechanical stability, thermoplastic infiltration and surface quality and processing costs were obtained for TiO2 nanotube layers containing TiO2 nanotubes of 1 micrometer length, annealed at 450oC in forming gas for 1 hour, employing Polycarbonate and Polypropilene thermoplastics.
v) Addition of an intermediate Au contact inside the nanocomposite. The inclusion of an intermediate electrical contact between the TiO2 nanotube layer and the thermoplastic was critical for the envisaged architecture of the solar cell. We metalized the of the TiO2 nanotube layer with tens of nanometer thick Au as electrical contact, prior to the nanocomposite synthesis. We validated this technical approach and verified that no additional issues aroused from the nanocomposite synthesis including this Au contact.
2.- The synthesis of Perovskite (CH3NH3PbI3) thin films and their infiltration inside the TiO2 nanotubes of the nanocomposites. The performed activities were:
i) Synthesis of perovskites thin films following and using reported reagents and protocols and, using commercial air compatible precursor inks. The best results in terms of reproducibility and envisaged scaling-up production were obtained from commercial precursor inks.
ii) Infiltration of Perovskite absorber inside the TiO2 nanotubes of the composites. We proceed to test different conditions for the infiltration of perovskite adsorber inside the TiO2 nanotubes of the composites. The results showed that composites based on Polycarbonate suffer degradation due to the solvent included with the Perovskite precursor ink. However nanocomposites based on polypropylene did not suffer noticeable degradation during the infiltration of the precursor ink.
3.- Deposition of Hole Transport Material and contacting. The performed activities were:
i) Deposition of HTM (Spiro-OMeoTaD) by reported protocols and the preliminary characterization of the solar cell. After the deposition of HTM and contacting some preliminary characterization (morphological, compositional and electronic) of the obtained solar cells were performed. The morphological characterization revealed heterogeneities in the HTM deposited layer. We ascribe these results to a not optimized deposition of HTM or a degradation of Perovskite material during the processing. However, the cross sectional images obtained by scanning electron microscopy (morphology and composition) revealed zones with the proposed optimal architecture (Figure 2). This fact points to the viability of the proposed fabrication method to obtain the envisaged flexible solar cells.
The obtained results showed the viability of the proposed fabrication method to obtain low cost solar cells based on TiO2 nanotubes, Pervoskites and thermoplastics.
Figure 2: Cross-sectional micrographs of the obtained solar cells a)Topography b) Compositional
Figure 1: Proposed Architecture and fabrication steps