TY  - JOUR
A1  - Vollbrecht, Joachim
A1  - Brus, Viktor V.
T1  - On charge carrier density in organic solar cells obtained via capacitance spectroscopy
JF  - Advanced electronic materials
N2  - The determination of the voltage-dependent density of free charge carriers via capacitance spectroscopy is considered an important step in the analysis of emerging photovoltaic technologies, such as organic and perovskite solar cells. In particular, an intimate knowledge of the density of free charge carriers is required for the determination of crucial parameters such as the effective mobility, charge carrier lifetime, nongeminate recombination coefficients, average extraction times, and competition factors. Hence, it is paramount to verify the validity of the commonly employed approaches to obtain the density of free charge carriers. The advantages, drawbacks, and limitations of the most common approaches are investigated in detail and strategies to mitigate misleading values are explored. To this end, two types of nonfullerene organic solar cells based on a PTB7-Th:ITIC-2F blend and a PM6:Y6 blend, respectively, are used as a case study to assess how subsequent analyses of the nongeminate recombination dynamics depend on the chosen approach to calculate the density of free charge carriers via capacitance spectroscopy.
KW  - bulk-heterojunction solar cells
KW  - capacitance spectroscopy
KW  - charge
KW  - carrier density
KW  - impedance spectroscopy
KW  - organic photovoltaics
Y1  - 2020
U6  - https://doi.org/10.1002/aelm.202000517
SN  - 2199-160X
VL  - 6
IS  - 10
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Vollbrecht, Joachim
A1  - Brus, Viktor V.
T1  - On the recombination order of surface recombination under open circuit conditions
JF  - Organic electronics : physics, materials and applications
N2  - Understanding the recombination dynamics of organic and perovskite solar cells has been a crucial prerequisite in the steadily increasing performance of these promising new types of photovoltaics. Surface recombination in particular has turned out to be one of the last remaining roadblocks, which specifically reduces the open circuit voltage. In this study, the relationship between the rate of surface recombination and the density of charge carriers is analyzed, revealing a cubic dependence between these two parameters. This hypothesis is then tested and verified with the recombination dynamics of an organic solar cell known to exhibit significant surface recombination and a high energy proton irradiated CH3NH3PbI3 pemvskite solar cell during white light illumination. Incidentally, these results can also explain recombination orders exceeding the commonly known threshold for bimolecular recombination that have been observed in some studies without the need for a charge carrier dependent bimolecular recombination coefficient.
KW  - surface recombination
KW  - recombination order
KW  - organic photovoltaics
KW  - Perovskite solar cells
KW  - charge carrier density
KW  - Shockley-Read-Hall
KW  - statistics
Y1  - 2020
U6  - https://doi.org/10.1016/j.orgel.2020.105905
SN  - 1566-1199
SN  - 1878-5530
VL  - 86
PB  - Elsevier Science
CY  - Amsterdam [u.a.]
ER  -