Publication date: 15th December 2025
Solar fuel production by photocatalysis is becoming more and more efficient and economic, especially when driven by earth abundant and organic materials. In this talk, we present ways to probe and tailor (ion-enhanced) light-mater interactions in organic photocatalysts in general, and 2D CNx in particular, in order to yield beneficial solar energy conversion properties.
While organics’ bottom-up design possibilities promise tailorable structure-function relationships for enhanced activity, the advancement is often hindered by limiting knowledge of interwoven photo-physical processes and properties that lead to recombination losses.[1] I will explain how different time-resolved (transient) spectroscopy techniques in combination with varying environmental conditions can be used to provide insights into the very beginning of the solar energy conversion process chain, focussing on exciton generation and separation, and charge stabilization being responsible for most efficiency losses. This enables to better understand light-matter interactions, and to tailor them to address bottlenecks associated with exciton recombination, especially occurring in organic materials.
We introduce Terahertz-Time Domain Spectroscopy (THz-TDS) measurements as convenient technique to probe the complex permittivity, and with that the dielectric properties of organic semiconductors on the very ps-time scales. The dielectric response defines exciton binding and is hence relevant for charge carrier photogeneration in all solar energy conversion technologies, but its values are highly frequency dependent, and commonly extracted at timescales orders magnitude off the ps-regime. Our study focussing on carbon nitrides now reveals dielectric screening and transport properties at the early time scales of solar energy conversion process chains. At the same time, it shows that also in this ultrafast regime, the environment and ions can matter, and strongly enhance photophysical parameters.[2]
Second, we present novel insight to ultrafast time resolved transient optical spectroscopies on 2D CNx, shedding light on their uncommon and environmentally dependent pathways to generate charges for photocatalytic energy conversion.
Keywords: photocatalysis, organic semiconductors, poly(heptazine imides), excitonic properties, ultrafast spectroscopy
References:
[1] T. Banerji, F. Podjaski, J. Kröger et al.: Polymer photocatalysts for solar-to-chemical energy conversion. Nat. Rev. Mater. 6, 168–190 (2021).
[2] R. Jahangir, F. Podjaski*, P. Alimard, S. A. J. Hillman, S. Davidson, S. Stoica, A. Kafizas, M. Naftaly, J. R. Durrant: Terahertz-permittivity of Carbon Nitrides: Revealing humidity-enhanced dielectric properties on the picosecond timescales relevant for charge carrier photogeneration. Under revision. Preprint: https://www.arxiv.org/abs/2411.06226.
[3] Menghan Xu, Samuel Hillman, F. Podjaski, J. Durrant et al., In preparation.
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