Instability in CH3NH3PbI3 perovskite solar cells due to elemental migration and chemical composition changes

Organic-inorganic halide perovskites have rapidly grown as favorable materials for photovoltaic applications, but accomplishing long-term stability is still a major research problem. This work demonstrates a new insight on instability and degradation factors in CH3NH3PbI3 perovskite solar cells aging with time in open air. X-ray photoelectron spectroscopy (XPS) has been used to investigate the compositional changes caused by device degradation over the period of 1000 hrs. XPS spectra confirm the migration of metallic ions from the bottom electrode (ITO) as a key factor causing the chemical composition change in the perovskite layer besides the diffusion of oxygen. XPS results are in good agreement with the crystallographic marks. Glow discharge optical emission spectrometry (GD-OES) has also been performed on the samples to correlate the XPS results. Based on the experimental results, fundamental features that account for the instability in the perovskite solar cell is discussed. - 2017 The Author(s).The authors are thankful to the Center for Advanced Materials (CAM), Qatar University for the laboratory support during the experimental work. The authors are also grateful to the Gas Processing Center (GPC), Qatar University for providing the XPS analysis facility. Thanks to HORIBA Scientific – Jocelyne Marciano, Sofia Gaiaschi and Patrick Chapon for the GD measurements and interpretation. This publication was also made possible by NPRP grant # 6-175-2-070 from Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Growth of MAPbBr3 perovskite crystals and its interfacial properties with Al and Ag contacts for perovskite solar cells

In this work, the MAPbBr3 perovskite crystals were grown and the interfacial properties of the poly-crystalline MAPbBr3 with Aluminum (Al) and Silver (Ag) contacts has been investigated. MAPbBr3 crystals are turned into the poly-crystalline pellets (PCP) using compaction technique and the Al/PCP, Al/interface layer/PCP, Ag/PCP, and Ag/interface layer/PCP contacts were investigated. Scanning Electron Microscopic (SEM), Energy-dispersive X-ray spectroscopy (EDX) and current-voltage (I-V) characteristic technique were used to have an insight of the degradation mechanism happening at the Metal/perovskite interface. The Ag/PCP contact appears to be stable, whereas Al is found to be highly reactive with the MAPbBr3 perovskite crystals due to the infiltration setback of Al in to the perovskite crystals. The interface layer showed a slight effect on the penetration of Al in to the perovskite crystals however it does not seem to be an appropriate solution. It is noteworthy that the stability of the underlying metal/perovskite contact is very crucial towards the perovskite solar cells with extended device lifetime. 1 2017 Elsevier B.V.The authors are thankful to the Center for Advanced Materials (CAM), Qatar University for the support during this work. This publication was partially made possible by NPRP grant # 6-175-2-070 from Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Effect of microwave sintering on the crystal domain and electrical properties of TiO2 nanoparticles

We report the effect of microwaves sintering on the crystal domain and electrical properties of TiO2 nanoparticles. Commercially available TiO2 nanoparticles of 25 nm size were coated on ITO (indium tin oxide) substrates, which were then sintered at 450 C employing microwave and conventional sintering approaches. The structural properties of the sintered coatings were examined using atomic force microscopy (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS), whereas the charge transfer properties were investigated using electrochemical impedance spectroscopy (EIS). Structural analysis reveals that the microwave sintering of TiO2-coated substrates results in the formation of more ordered crystal structure as compared to the conventionally sintered samples. Nyquist plots demonstrate the improved charge transfer characteristics of TiO2 nanoparticles in microwave-sintered layers. Also, the application of the microwave-sintered TiO2-coated ITO substrates as photoanode in dye-sensitized solar cells (DSSCs) confirms superior electrical properties compared to conventionally sintered samples.Scopu