Abstract
The primary objective of this proposal is to understand the impact of the preparation conditions upon the formation of the hybrid perovskite materials and develop strategies to improve the stability of the solar cells under ambient conditions.Recently, organicinorganic hybrid perovskite solar cells (PSCs) have emerged as attractive candidate for thin-film photovoltaic devices due to their high performance and low cost. The perovskite crystal structure, ABX3 (where A, B, and X are an organic cation (CH3NH3+(MA), NH2CH=NH2+(FA), metal cation (Pb2+, Sn2+) and halide anion (Cl-, Br- or I-)), respectively, renders exceptional properties to this material. The band gap can be tuned from the ultraviolet to infrared region through varying the components and ratio between them. Perovskite materials have high extinction coefficients (e.g. comparable to GaAs), direct bandgap and they exhibit both electron and hole charge carrier mobility, and exceptionally long charge carrier diffusion lengths. The state-of-art of the PSCs relies in devices with efficiency of 22%.Although the rapid growth of PSCs, which is accompanied by the impressive values of efficiency, make them the most studied topic between the emergent solar cells, several aspects in this technology must be overcome for future implementation. These include the replacement of lead (Pb), the low stability perovskite under ambient conditions, hysteresis in the devices, and expensive components as gold or Spiro-OMEOTAD contacts. Besides, the formation of the perovskite materials, especially in ambient conditions, although very desired, is not well understood. Several reports have indicated the positive influence of water uptake during the crystallization of the perovskite film. Therefore, a strong focus in this project will be placed on the understanding of formation of hybrid perovskite materials under different atmospheres (air and nitrogen) and applying different heating protocols. We will mainly focus on mixed cations hybrid perovskites (MAFAPbX3, CsFAMAPbX3, RbCsFAMAPbX3) a new family of hybrid perovskites that have allowed the fabrication of solar cells with PCE above 20% with improved thermal stability. The preparation of this class of perovskites is currently carried out inside the Glove Box and there are no reports about the influence of preparation conditions on the crystalline structure, morphology and correlation with device's performance. A dry atmosphere (significantly increases equipment and operational costs for(industrial processes, so ambient perovskite fabrication will be(less expensive and more attractive.Toney's group at Stanford Synchrotron Radiation Lightsource at the SLAC National Accelerator Laboratory (SLAC) has employed X-ray absorption spectroscopy, X-ray fluorescence and X-ray diffraction techniques to probe the(formation, phase transitions and composition in perovskite materials.We expect that the proposed approach, using the techniques available at SLAC will allow gaining unprecedented insight into the fundamental aspects of the formation of the perovskite crystalline structure and film morphology under different preparation conditions (air and nitrogen at different temperatures). This collaboration is based on recent results obtained at University of Campinas on the formation of the perovskite materials and also on the stability under ambient conditions.
|