TY  - JOUR
A1  - Benduhn, Johannes
A1  - Piersimoni, Fortunato
A1  - Londi, Giacomo
A1  - Kirch, Anton
A1  - Widmer, Johannes
A1  - Koerner, Christian
A1  - Beljonne, David
A1  - Neher, Dieter
A1  - Spoltore, Donato
A1  - Vandewal, Koen
T1  - Impact of triplet excited states on the open-circuit voltage of organic solar cells
JF  - dvanced energy materials
N2  - The best organic solar cells (OSCs) achieve comparable peak external quantum efficiencies and fill factors as conventional photovoltaic devices. However, their voltage losses are much higher, in particular those due to nonradiative recombination. To investigate the possible role of triplet states on the donor or acceptor materials in this process, model systems comprising Zn- and Cu-phthalocyanine (Pc), as well as fluorinated versions of these donors, combined with C-60 as acceptor are studied. Fluorination allows tuning the energy level alignment between the lowest energy triplet state (T-1) and the charge-transfer (CT) state, while the replacement of Zn by Cu as the central metal in the Pcs leads to a largely enhanced spin-orbit coupling. Only in the latter case, a substantial influence of the triplet state on the nonradiative voltage losses is observed. In contrast, it is found that for a large series of typical OSC materials, the relative energy level alignment between T-1 and the CT state does not substantially affect nonradiative voltage losses.
KW  - charge-transfer states
KW  - nonradiative voltage losses
KW  - organic solar cells
KW  - triplet excited states
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201800451
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 21
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Krückemeier, Lisa
A1  - Rau, Uwe
A1  - Stolterfoht, Martin
A1  - Kirchartz, Thomas
T1  - How to report record open-circuit voltages in lead-halide perovskite solar cells
JF  - Advanced energy materials
N2  - Open-circuit voltages of lead-halide perovskite solar cells are improving rapidly and are approaching the thermodynamic limit. Since many different perovskite compositions with different bandgap energies are actively being investigated, it is not straightforward to compare the open-circuit voltages between these devices as long as a consistent method of referencing is missing. For the purpose of comparing open-circuit voltages and identifying outstanding values, it is imperative to use a unique, generally accepted way of calculating the thermodynamic limit, which is currently not the case. Here a meta-analysis of methods to determine the bandgap and a radiative limit for open-circuit voltage is presented. The differences between the methods are analyzed and an easily applicable approach based on the solar cell quantum efficiency as a general reference is proposed.
KW  - bandgap
KW  - fill factor losses
KW  - nonradiative voltage losses
KW  - photovoltaics
KW  - radiative limit
KW  - recombination
KW  - Shockley-Queisser model
Y1  - 2019
U6  - https://doi.org/10.1002/aenm.201902573
SN  - 1614-6832
SN  - 1614-6840
VL  - 10
IS  - 1
PB  - Wiley-VCH
CY  - Weinheim
ER  -