TY  - JOUR
A1  - Baumann, A.
A1  - Tvingstedt, K.
A1  - Heiber, M. C.
A1  - Väth, S.
A1  - Momblona, C.
A1  - Bolink, H. J.
A1  - Dyakonov, V.
T1  - Persistent photovoltage in methylammonium lead iodide perovskite solar cells
JF  - APL Materials
N2  - We herein perform open circuit voltage decay (OCVD) measurements on methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells to increase the understanding of the charge carrier recombination dynamics in this emerging technology. Optically pulsed OCVD measurements are conducted on CH3NH3PbI3 solar cells and compared to results from another type of thin-film photovoltaics, namely, the two reference polymer–fullerene bulk heterojunction solar cell devices based on P3HT:PC60BM and PTB7:PC70BM blends. We observe two very different time domains of the voltage transient in the perovskite solar cell with a first drop on a short time scale that is similar to the decay in the studied organic solar cells. However, 65%–70% of the maximum photovoltage persists on much longer timescales in the perovskite solar cell than in the organic devices. In addition, we find that the recombination dynamics in all time regimes are dependent on the starting illumination intensity, which is also not observed in the organic devices. We then discuss the potential origins of these unique behaviors.
KW  - solar cells
KW  - illumination
KW  - dielectric oxides
KW  - carrier density
KW  - bioelectrochemistry
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119397
VL  - 2
IS  - 8
ER  - 
TY  - JOUR
A1  - Kiermasch, David
A1  - Rieder, Philipp
A1  - Tvingstedt, Kristofer
A1  - Baumann, Andreas
A1  - Dyakonov, Vladimir
T1  - Improved charge carrier lifetime in planar perovskite solar cells by bromine doping
JF  - Scientific Reports
N2  - The charge carrier lifetime is an important parameter in solar cells as it defines, together with the mobility, the diffusion length of the charge carriers, thus directly determining the optimal active layer thickness of a device. Herein, we report on charge carrier lifetime values in bromine doped planar methylammonium lead iodide (MAPbI\(_3\)) solar cells determined by transient photovoltage. The corresponding charge carrier density has been derived from charge carrier extraction. We found increased lifetime values in solar cells incorporating bromine compared to pure MAPbI\(_3\) by a factor of ~2.75 at an illumination intensity corresponding to 1 sun. In the bromine containing solar cells we additionally observe an anomalously high value of extracted charge, which we deduce to originate from mobile ions.
KW  - devices for energy harvesting
KW  - solar cells
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-147976
VL  - 6
ER  - 
TY  - JOUR
A1  - Kraus, Hannes
A1  - Heiber, Michael C.
A1  - Väth, Stefan
A1  - Kern, Julia
A1  - Deibel, Carsten
A1  - Sperlich, Andreas
A1  - Dyakonov, Vladimir
T1  - Analysis of Triplet Exciton Loss Pathways in PTB7:PC\(_{71}\)BM Bulk Heterojunction Solar Cells
JF  - Scientific Reports
N2  - A strategy for increasing the conversion efficiency of organic photovoltaics has been to increase the VOC by tuning the energy levels of donor and acceptor components. However, this opens up a new loss pathway from an interfacial charge transfer state to a triplet exciton (TE) state called electron back transfer (EBT), which is detrimental to device performance. To test this hypothesis, we study triplet formation in the high performing PTB7:PC\(_{71}\)BM blend system and determine the impact of the morphology-optimizing additive 1,8-diiodoctane (DIO). Using photoluminescence and spin-sensitive optically detected magnetic resonance (ODMR) measurements at low temperature, we find that TEs form on PC\(_{71}\)BM via intersystem crossing from singlet excitons and on PTB7 via EBT mechanism. For DIO blends with smaller fullerene domains, an increased density of PTB7 TEs is observed. The EBT process is found to be significant only at very low temperature. At 300 K, no triplets are detected via ODMR, and electrically detected magnetic resonance on optimized solar cells indicates that TEs are only present on the fullerenes. We conclude that in PTB7:PC\(_{71}\)BM devices, TE formation via EBT is impacted by fullerene domain size at low temperature, but at room temperature, EBT does not represent a dominant loss pathway.
KW  - solar cells
KW  - electronic properties and materials
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-147413
VL  - 6
IS  - 29158
ER  - 
TY  - JOUR
A1  - Tvingstedt, Kristofer
A1  - Malinkiewicz, Olga
A1  - Baumann, Andreas
A1  - Deibel, Carsten
A1  - Snaith, Henry J.
A1  - Dyakonov, Vladimir
A1  - Bolink, Henk J.
T1  - Radiative efficiency of lead iodide based perovskite solar cells
JF  - Scientific Reports
N2  - The maximum efficiency of any solar cell can be evaluated in terms of its corresponding ability to emit light. We herein determine the important figure of merit of radiative efficiency for Methylammonium Lead Iodide perovskite solar cells and, to put in context, relate it to an organic photovoltaic (OPV) model device. We evaluate the reciprocity relation between electroluminescence and photovoltaic quantum efficiency and conclude that the emission from the perovskite devices is dominated by a sharp band-to-band transition that has a radiative efficiency much higher than that of an average OPV device. As a consequence, the perovskite have the benefit of retaining an open circuit voltage ~0.14 V closer to its radiative limit than the OPV cell. Additionally, and in contrast to OPVs, we show that the photoluminescence of the perovskite solar cell is substantially quenched under short circuit conditions in accordance with how an ideal photovoltaic cell should operate.
KW  - solar cells
KW  - optical spectroscopy
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119360
VL  - 4
ER  - 
TY  - JOUR
A1  - Wen, Xinbo
A1  - Nowak-Król, Agnieszka
A1  - Nagler, Oliver
A1  - Kraus, Felix
A1  - Zhu, Na
A1  - Zheng, Nan
A1  - Müller, Matthias
A1  - Schmidt, David
A1  - Xie, Zengqi
A1  - Würthner, Frank
T1  - Tetrahydroxy-perylene bisimide embedded in zinc oxide thin film as electron transporting layer for high performance non-fullerene organic solar cells
JF  - Angewandte Chemie International Edition
N2  - By introduction of four hydroxy (HO) groups into the two perylene bisimide (PBI) bay areas, new HO‐PBI ligands were obtained which upon deprotonation can complex ZnII ions and photosensitize semiconductive zinc oxide thin films. Such coordination is beneficial for dispersing PBI photosensitizer molecules evenly into metal oxide films to fabricate organic–inorganic hybrid interlayers for organic solar cells. Supported by the photoconductive effect of the ZnO:HO‐PBI hybrid interlayers, improved electron collection and transportation is achieved in fullerene and non‐fullerene polymer solar cell devices, leading to remarkable power conversion efficiencies of up to 15.95 % for a non‐fullerene based organic solar cell.
KW  - hydroxylation
KW  - metal complexenes
KW  - perylene bisimide
KW  - photoconductive interlayer
KW  - solar cells
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204723
VL  - 58
IS  - 37
ER  -