TY - JOUR
T1 - Efficiency Limits in Wide-Bandgap Ge-Containing Donor Polymer:Nonfullerene Acceptor Bulk Heterojunction Solar Cells
AU - Alsaggaf, Sarah
AU - Ashraf, Raja Shahid
AU - Purushothaman, Balaji
AU - Chaturvedi, Neha
AU - McCulloch, Iain
AU - Laquai, Frédéric
AU - Khan, Jafar Iqbal
N1 - Publisher Copyright:
© 2021 Wiley-VCH GmbH.
PY - 2021/12
Y1 - 2021/12
N2 - A precise picture of the photophysics that determine the efficiency of nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic solar cells is still missing, yet needed to mitigate the remaining loss channels. Herein, charge carrier generation and recombination dynamics in blends of a novel wide-bandgap germanium-containing donor polymer, namely, PEHGeNDT-BT, paired with either O-IDTBR or O-IDTBCN as NFA in BHJ solar cells are investigated by (ultrafast) transient spectroscopy and time-delayed collection field (TDCF) experiments. Photovoltaic devices yield moderate power conversion efficiencies (PCEs) of 5.3% when using O-IDTBCN as the acceptor, and only about 2% when using O-IDTBR as the acceptor, the latter severely limited by its low photocurrent and moderate fill factor (FF) of ≈43%. Time-resolved photoluminescence experiments reveal limited exciton quenching as one loss channel in O-IDTBR-based blends, accompanied by significant geminate recombination further reducing the photocurrent, while field-dependent charge generation is identified as the origin of the low FF. Geminate recombination is less in the O-IDTBCN blend and charge generation is field-independent, leading to improved photocurrent and FF. Carrier drift-diffusion simulations of the devices’ current–voltage (J–V) characteristics confirm that the experimentally determined kinetic parameters and process yields can reproduce the measured J–V curves under steady-state solar illumination.
AB - A precise picture of the photophysics that determine the efficiency of nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic solar cells is still missing, yet needed to mitigate the remaining loss channels. Herein, charge carrier generation and recombination dynamics in blends of a novel wide-bandgap germanium-containing donor polymer, namely, PEHGeNDT-BT, paired with either O-IDTBR or O-IDTBCN as NFA in BHJ solar cells are investigated by (ultrafast) transient spectroscopy and time-delayed collection field (TDCF) experiments. Photovoltaic devices yield moderate power conversion efficiencies (PCEs) of 5.3% when using O-IDTBCN as the acceptor, and only about 2% when using O-IDTBR as the acceptor, the latter severely limited by its low photocurrent and moderate fill factor (FF) of ≈43%. Time-resolved photoluminescence experiments reveal limited exciton quenching as one loss channel in O-IDTBR-based blends, accompanied by significant geminate recombination further reducing the photocurrent, while field-dependent charge generation is identified as the origin of the low FF. Geminate recombination is less in the O-IDTBCN blend and charge generation is field-independent, leading to improved photocurrent and FF. Carrier drift-diffusion simulations of the devices’ current–voltage (J–V) characteristics confirm that the experimentally determined kinetic parameters and process yields can reproduce the measured J–V curves under steady-state solar illumination.
KW - charge carrier recombination
KW - nonfullerene acceptors
KW - organic photovoltaics
KW - quadrupole moment
KW - ultrafast spectroscopy
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U2 - 10.1002/pssr.202100206
DO - 10.1002/pssr.202100206
M3 - Article
AN - SCOPUS:85114374256
SN - 1862-6254
VL - 15
JO - Physica Status Solidi - Rapid Research Letters
JF - Physica Status Solidi - Rapid Research Letters
IS - 12
M1 - 2100206
ER -