Quantification of Photophysical Processes in All‐Polymer Bulk Heterojunction Solar Cells
byA. H. Balawi, Z. Kan, J. Gorenflot, P. Guarracino, N. Chaturvedi, A. Privitera, S. Liu, Y. Gao, L. Franco, P. Beaujuge, F. Laquai
Year:2020
Bibliography
Quantification of Photophysical Processes in All‐Polymer Bulk Heterojunction Solar Cells
A. H. Balawi, Z. Kan, J. Gorenflot, P. Guarracino, N. Chaturvedi, A. Privitera, S. Liu, Y. Gao, L. Franco, P. Beaujuge, F. Laquai
Solar RRL 2020, 2000181.
Abstract
All‐polymer solar cells lag behind the state‐of‐the‐art in small
molecule nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic
solar cells (OSCs) for reasons still unclear. Herein, the
efficiency‐limiting processes in all‐polymer solar cells are
investigated using blends of the common donor polymer PBDT‐TS1 with
different acceptor polymers, namely P2TPD[2F]T and P2TPDBT[2F]T.
Combining data from steady‐state optical spectroscopy and time‐resolved
photoluminescence, transient absorption, and time‐delayed collection
field experiments, provides not only a concise but also quantitative
assessment of the losses due to limited photon absorption, geminate and
nongeminate charge carrier recombination, field‐dependent charge
generation, and inefficient carrier extraction. Although both systems
exhibit a similar charge separation efficiency in the absence of
external bias, charge separation is significantly enhanced in
P2TPDBT[2F]T‐based blends when biased. Kinetic parameters obtained via
pulsed laser spectroscopy are used to reproduce the experimentally
measured device current–voltage (J–V) characteristics and
indicate that low fill factors originate either from nongeminate
recombination competing with charge extraction, or from a pronounced
field dependence of charge generation, depending on the acceptor
polymer. The methodology presented here is generic and can be used to
quantify the loss processes in BHJ OSCs including both all‐polymer and
small molecule NFA systems.
Keywords
All-polymer solar cellsbulk heterojunctionsNonfullerene acceptorsOrganic photovoltaicstransient absorption