SPP 2196 - Perovskite semiconductors: From fundamental properties to devices
A new class of hybrid organic-inorganic lead halide perovskite semiconductors has attracted global attention since the reports on high efficiency perovskite solar cells in mid-2012. In only a few years photoconversion efficiency surpassing 22% has been achieved. Despite rapid progress in this emerging field, there is limited understanding of the basic mechanisms that lead to such an extraordinary performance. Due to continuing optimization strategies, the originally simple perovskite crystal structure is getting more and more complex, leading to new challenges regarding phase and interface behaviour. Also, degradation mechanisms and the role of the toxic lead (and its replacement in high performing devices) are not clear.
Researchers worldwide have started to unravel the peculiar properties of these materials and devices, the role and interplay of their different components, and the control over the parameters dominating the solar cell performance. For exploiting the full potential of this new and exciting class of semiconductor, in solar-cell research and beyond, a concerted effort is needed to establish a fundamental and reliable knowledge base. The focus of the SPP is on the investigation of fundamental working mechanisms. This includes structural, optical, electronic, and magnetic properties and, most importantly, their correlations.
Type and density of defects significantly affect the properties and function of a semiconductor leading to enhanced or reduced performance.
The application in photovoltaics or in optoelectronics requires in-depth knowledge of defect-property relationships. The project brings together expertise in chemical synthesis (S. Polarz, Uni Hanover), physics of semiconductor nanostructures (L. Schmidt-Mende Uni Konstanz) and spatially resolved electronic and optoelectronic measurements (S. Weber,
MPI-P) to tackle following tasks: (i) aerosol synthesis of MAPX (CH3NH3PbX3); (ii) role of crystal direction and facets on optical and electronic properties; (iii) role of controlled dopant concentration (stoichiometry), (iv) advanced functionalization of MAPX by inclusion of new dopants. We will apply techniques like conductive atomic force microscopy (C-AFM) and time-resolved Kelvin probe spectroscopy for clarification how the stoichiometry, presence of dopants and defects influence the local electrical and ionic conductivity. The effect of ferroelastic domains will be investigated on a single-particle level as well using piezoresponse force microscopy (PFM).