Seminar of Physics at Wrocław University of Technology
PWr, bud. A1, sala 322
Photothermal characterisation of optoelectronic materials: from fundamental properties to applications
dr Szymon J. Zelewski
Katedra Fizyki Doświadczalnej, Wydział Podstawowych Problemów Techniki, Politechnika Wrocławska Optoelectronics Group, Cavendish Laboratory, University of Cambridge, UK
The production of semiconductor devices based on new optically active materials relies on the ability to probe their fundamental properties with a level of sophistication that allows to predict their usefulness at the early stage of development. One such example is the correlation between the energetic disorder in photovoltaic absorbers and the power conversion efficiency of a full solar cell, albeit posing experimental challenges in terms of sensitive optical absorption coefficient measurements to reveal the Urbach tail. In this talk, I will present recent advancements in the field of photothermal spectroscopy, an experimental tool based on light-to-heat conversion through nonradiative recombination processes. Its unique features make it exceptionally useful for high dynamic range absorbance measurements of thin-film semiconductors, especially in the spectral range below the band gap. A complementary experimental arrangement comprising a combination of photothermal deflection spectroscopy (PDS) and external quantum efficiency (EQE) will be shown to point out challenges arising from device-level characterisation. The results provide new insights into the underlying mechanisms improving the performance of perovskite (2D and 3D) light-emitting diodes upon passivation of the active layer. For a broader context, I will showcase key findings related to photothermal measurements of other emerging optoelectronic materials, with a focus on conjugated polymers. The last part will include a demonstration of non-contact, fully optical probing of thermal transport parameters using experimental approaches under the same umbrella.
