Fe and Ti metal-organic frameworks: Towards tailored materials for photovoltaic applications

Abstract

Several metal-organic framework (MOF) materials have been recently employed in optoelectronic devices due to the unique properties of the MOF materials that result in enhanced performance and stability. In this work, the NH2-MIL-101(Fe) (1) and NH2-MIL-125(Ti) (2) MOFs were prepared using 2-aminoterephthalic acid as the ligand. The crystal structures were confirmed by powder X-ray diffraction and the morphology was examined by scanning electron microscopy. We obtained specific surface areas of 2563.66m2/g for sample (1) and 602.37m2/g for sample (2) using the Brunauer-Emmett-Teller theory. Films were obtained both by spin coating and liquid epitaxy deposition techniques, and the thickness, roughness and crystalline domains were obtained with atomic force microscopy. UV-vis spectroscopy showed the absorption of the MOF films with a band gap energy of 2.66 eV and 2.13 eV for (1) and (2), respectively. Both materials were employed as the electron transport layer in perovskite solar cells and after optimizing the MOF thickness in ambient perovskite device fabrication we achieved reasonable device efficiencies that allowed convoluting the performance parameters with the structural properties of the different materials. This work yields more evidence that MOFs are promising materials as electron transporting layers for perovskite solar cells that could allow the use of flexible substrates due to their low temperature processing.