Dr. Filippo De Angelis, Institute of Molecular Science and Technologies, University of Perugia, Italy.
An outstanding property of lead-halide perovskites is the incredibly low band-gap to open circuit voltage loss, which in optimized devices is close to the thermodynamic limit (1.6 eV gap; 1.3 V voltage, loss ~0.3 V). The high open circuit voltage is extremely attractive for both photovoltaics and water splitting. These observations suggest an apparently low density of traps in MAPbI3, contrary to the expectedly high defect density of a low-temperature, solution-processed material, suggesting that metal halide perovskites are inherently defect tolerant due to dominant defects introducing only shallow traps in the material band-gap. A mechanism for the protection of charge carriers implying large polarons has also been invoked to explain the long carrier lifetimes and diffusion lengths favoring efficient carrier collection at selective contacts, leading to power conversion efficiencies competing with established thin film photovoltaics. 
We present on overview of first-principles computational analyses devoted to understanding the outstanding optoelectronic properties of lead-halide perovskites. We show that despite the fairly high defect density due to lead and MA-related defects, only less abundant iodine defects introduce deep electron and hole traps in MAPbI3.[3-5] The peculiar iodine redox chemistry leads, however, to kinetic deactivation of filled electron traps, leaving short-lived hole traps as potentially harmful defects.[6,7] Hole traps can be eventually converted to electron traps under mild oxidizing conditions, clarifying the defect tolerance. A polaronic mechanism, triggered by a photoinduced structural deformation, is presented which is also responsible for the reduced electron/hole recombination observed in lead-halide perovskites. [8,9]
The two ingredients, intimately related to the constituting lead-halide chemistry, represent the key to the success of perovskite-based PV and can represent the basis for development of new materials with similar target characteristics, possibly avoiding the environmental risks posed by lead.
1. E. H. Anaraki et al. Energy Environ. Sci. 2016, 9, 3128.
2. W. J. Yin et al. Appl. Phys. Lett. 2014, 104, 063903.
3. D. Meggiolaro et al. ACS Energy Lett., 2017, 2, 2794.
4. E. Mosconi et al. Energy Environ. Sci. 2016, 9, 3180.
5. D. Meggiolaro et al. ACS Energy Lett., 2018, 3, 447.
6. D. Meggiolaro et al. Energy Environ. Sci., 2018, 11, 702.
7. F. De Angelis, A. Petrozza Nat. Mater. 2018, 17, 377.
8. K. Miyata et al. Sci. Adv. 2017, 3, e1701217.
9. F. Ambrosio et al. Energy Environ. Sci., 2018, 11, 101.
Filippo De Angelis is a Senior Research Scientist and deputy director at the CNR Institute of Molecular Sciences and Technology, in Perugia, Italy. He is the founder and co-leader of the Computational Laboratory for Hybrid/Organic Photovoltaics in Perugia. He earned a BS in Chemistry 1996 and a PhD in Theoretical Inorganic Chemistry in 1999, both from the University of Perugia, Italy. He is an expert in the development and application of first principles computational methods to the simulation of the structural, electronic and optical properties of metallorganic, inorganic and hybrid materials and molecules and related interfaces. The main application studies are in the field of solar energy materials, with emphasis on dye-sensitized and perovskite solar cells. His main contribution constitutes in the study of the excited states of dyes and perovskite absorbers, in the modelling of inorganic semiconductors and in the alignment of energy levels at sensitized semiconductor interfaces. Additional areas of expertise are in the field of non-linear optics, luminescent materials for OLEDs and organometallic reactivity and catalysis. He is the 2007 recipient of the Raffaello Nasini Gold Medal of the Inorganic Chemistry Division of the Italian Chemical Society.
Dr Filippo De Angelis is co-author of more than 300 peer-reviewed scientific papers bringing his h-index to 74 (>22 000 overall citations).