TY  - JOUR
A1  - Pranav, Manasi
A1  - Hultzsch, Thomas
A1  - Musiienko, Artem
A1  - Sun, Bowen
A1  - Shukla, Atul
A1  - Jaiser, Frank
A1  - Shoaee, Safa
A1  - Neher, Dieter
T1  - Anticorrelated photoluminescence and free charge generation proves field-assisted exciton dissociation in low-offset PM6:Y5 organic solar cells
JF  - APL materials : high impact open access journal in functional materials science
N2  - Understanding the origin of inefficient photocurrent generation in organic solar cells with low energy offset remains key to realizing high-performance donor-acceptor systems. Here, we probe the origin of field-dependent free-charge generation and photoluminescence in wnon-fullereneacceptor (NFA)-based organic solar cells using the polymer PM6 and the NFA Y5-a non-halogenated sibling to Y6, with a smaller energetic offset to PM6. By performing time-delayed collection field (TDCF) measurements on a variety of samples with different electron transport layers and active layer thickness, we show that the fill factor and photocurrent are limited by field-dependent free charge generation in the bulk of the blend. We also introduce a new method of TDCF called m-TDCF to prove the absence of artifacts from non-geminate recombination of photogenerated and dark charge carriers near the electrodes. We then correlate free charge generation with steady-state photoluminescence intensity and find perfect anticorrelation between these two properties. Through this, we conclude that photocurrent generation in this low-offset system is entirely controlled by the field-dependent dissociation of local excitons into charge-transfer states. (c) 2023 Author(s).
Y1  - 2023
U6  - https://doi.org/10.1063/5.0151580
SN  - 2166-532X
VL  - 11
IS  - 6
PB  - AIP Publishing
CY  - Melville
ER  - 
TY  - JOUR
A1  - Pena-Camargo, Francisco
A1  - Thiesbrummel, Jarla
A1  - Hempel, Hannes
A1  - Musiienko, Artem
A1  - Le Corre, Vincent M.
A1  - Diekmann, Jonas
A1  - Warby, Jonathan
A1  - Unold, Thomas
A1  - Lang, Felix
A1  - Neher, Dieter
A1  - Stolterfoht, Martin
T1  - Revealing the doping density in perovskite solar cells and its impact on device performance
JF  - Applied physics reviews
N2  - Traditional inorganic semiconductors can be electronically doped with high precision. Conversely, there is still conjecture regarding the assessment of the electronic doping density in metal-halide perovskites, not to mention of a control thereof. This paper presents a multifaceted approach to determine the electronic doping density for a range of different lead-halide perovskite systems. Optical and electrical characterization techniques, comprising intensity-dependent and transient photoluminescence, AC Hall effect, transfer-length-methods, and charge extraction measurements were instrumental in quantifying an upper limit for the doping density. The obtained values are subsequently compared to the electrode charge per cell volume under short-circuit conditions ( CUbi/eV), which amounts to roughly 10(16) cm(-3). This figure of merit represents the critical limit below which doping-induced charges do not influence the device performance. The experimental results consistently demonstrate that the doping density is below this critical threshold 10(12) cm(-3), which means << CUbi / e V) for all common lead-based metal-halide perovskites. Nevertheless, although the density of doping-induced charges is too low to redistribute the built-in voltage in the perovskite active layer, mobile ions are present in sufficient quantities to create space-charge-regions in the active layer, reminiscent of doped pn-junctions. These results are well supported by drift-diffusion simulations, which confirm that the device performance is not affected by such low doping densities.
Y1  - 2022
U6  - https://doi.org/10.1063/5.0085286
SN  - 1931-9401
VL  - 9
IS  - 2
PB  - AIP Publishing
CY  - Melville
ER  -