Charge Transport & Defect States

The optoelectronic performance of a semiconductor heavily depends on the ease with which its charge carriers move, as well as on the presence of defect states within its band gap. For instance, high photovoltaic efficiency requires photocarriers to speedily reach the collecting electrodes without undergoing recombination mediated by defect states. Therefore, the experimental characterisation of charge transport and defect states in emerging semiconductors is key to assessing and realizing their optoelectronic potential.

Prof. Pecunia has extensive experience in the experimental characterisation of charge transport and defect states in emerging solution-processible optoelectronic materials. His expertise in this area builds on his investigations of charge transport and trap states in organic and amorphous-metal-oxide semiconductors, primarily relying on field-effect transistor measurements and Scanning Kelvin Probe Microscopy (SKPM). 

At the Pecunia Research Group, we are interested in gaining insight into the charge transport and defect properties of metal-halide perovskites and derivatives, which constitute a large family of emerging solution-processible semiconductors with attractive technological prospects. To this end, we have established an experimental suite for the characterisation of carrier mobility via the Hall effect, and the determination of defect parameters via deep-level transient spectroscopy. By studying how charge transport and defects are influenced by variations in material composition, crystallographic properties, and microstructure, we gain insight into relevant structure-property relations. In turn, this allows us to rationalise key trends in optoelectronic behaviour as well as to identify materials and processing strategies towards high optoelectronic device performance. Ultimately, our aim is to identify rational criteria for the development of green metal-halide perovskites with high carrier mobility and good defect tolerance for next-generation optoelectronics and photovoltaics.

Charge Transport & Defect States

a) Characterisation of minority-carrier transport in organic semiconductors via Scanning Kelvin Probe Microscopy (10.1002/adma.201503812).

b) Schematic trap distributions in lead-free perovskite-inspired Ag2BiI5 layers deposited with a HI-additive (HIA) method and a hot-coating (HC) method (10.1007/s40820-020-0371-0).

c) Deep-level spectroscopy of the defect states in lead-free perovskite-inspired thin-films (10.1002/aenm.202003968).

Representative Publications

V. Pecunia†, J. Zhao, C. Kim, B. R. Tuttle, J. Mei, F. Li, Y. Peng, T. Huq, R. L.Z. Hoye, N. D. Kelly, S. E. Dutton, K. Xia, J. MacManus-Driscoll, H. Sirringhaus, Assessing the Impact of Defects on Lead-Free Perovskite-Inspired Photovoltaics via Photoinduced Current Transient Spectroscopy, Advanced Energy Materials, 11, 22, 2003968, 2021. DOI: 10.1002/aenm.202003968

F. Li*, Y. Wang, K. Xia, R. L. Z. Hoye, V. Pecunia†*, Microstructural and Photoconversion Efficiency Enhancement of Compact Films of Lead-Free Perovskite Derivative Rb3Sb2I9, Journal of Materials Chemistry A, 8, 4396–4406, 2020. DOI: 10.1039/C9TA13352F

V. Pecunia†*, Y. Yuan*, J. Zhao, K. Xia, Y. Wang, S. Duhm, L. Portilla, F. Li, Perovskite-Inspired Lead-Free Ag2BiI5 for Self-Powered NIR-Blind Visible Light Photodetection, Nano-Micro Letters, 12:27, 2020. DOI: 10.1007/s40820-020-0371-0

V. Pecunia†*, M. Nikolka*, A. Sou, I. Nasrallah, A. Y. Amin, I. McCulloch, H. Sirringhaus†, Trap Healing for High-Performance Low-Voltage Polymer Transistors and Solution-Based Analog Amplifiers on Foil, Advanced Materials, 29, 1606938, 2017. DOI: 10.1002/adma.201606938

Y. Hu*, V. Pecunia*, L. Jiang, C. Di, X. Gao, H. Sirringhaus†, Scanning Kelvin Probe Microscopy Investigation of the Role of Minority Carriers on the Switching Characteristics of Organic Field-Effect Transistors, Advanced Materials, 28, 4713–4719, 2016. DOI: 10.1002/adma.201503812

D. Venkateshvaran*, M. Nikolka*, A. Sadhanala, V. Lemaur, M. Zelazny, M. Kepa, M. Hurhangee, A. J. Kronemeijer, V. Pecunia, I. Nasrallah, I. Romanov, K. Broch, I. McCulloch, D. Emin, Y. Olivier, J. Cornil, D. Beljonne, H. Sirringhaus†, Approaching Disorder-Free Transport in High-Mobility Conjugated Polymers, Nature, 515, 384–388, 2014. DOI: 10.1038/nature13854

J. Kronemeijer†, V. Pecunia, D. Venkateshvaran, M. Nikolka, A. Sadhanala, J. Moriarty, M. Szumilo, H. Sirringhaus†, Two-Dimensional Carrier Distribution in Top-Gate Polymer Field-Effect Transistors: Correlation between Width of Density of Localized States and Urbach Energy, Advanced Materials, 26, 728–733, 2014.DOI: 10.1002/adma.201303060