Natalie Banerji1
University of Bern1
Organic conjugated materials have many favourable properties that make them interesting for a variety of electronic applications. The aim of my group is to understand the fundamental processes underlying their functionality. We use ultrafast spectroscopic techniques, such as transient absorption (TA) and time-domain terahertz (TD-THz) spectroscopies, to investigate charge carriers in organic semiconductors. While femtosecond TA measurements bring insights to the nature and evolution of the photoexcited species, we use TD-THz spectroscopy to gain information about the charge transport properties on the nanoscale. After presenting an overview of our experimental techniques, I will show results about charge generation in highly efficient solar cell materials based on organic polymer:fullerene [1] polymer:non-fullerene blends [2] with negligible driving force for interfacial charge transfer. Efficiencies beyond 18% have recently been achieved by combining low bandgap conjugated polymers with small-molecule non-fullerene acceptors (NFAs). I will discuss how charge generation and recombination processes depend on parameters such as the charge transfer driving force, the short-range charge mobility and the morphology.<br/>[1] R. Shivhare, G. J. Moore, A. Hofacker, S. Hutsch, Y. Zhong, M. Hambsch, T. Erdmann, A. Kiriy, S. C.B. Mannsfeld, F. Ortmann, N. Banerji. Advanced Materials (2021), 2101784 .<br/>[2] Y. Zhong, M. Causa’, G. J. Moore, P. K., B. Xiao, F. Günther, J. Kublitski, R. Shivhare, J. Benduhn, E. BarOr, S. Mukherjee, K. M. Yallum, J. Réhault, S.C.B. Mannsfeld, D. Neher, L. J. Richter, D. M. DeLongchamp, F. Ortmann, K. Vandewal, E. Zhou, N. Banerji. Nature Communications (2020), 11, 833