TY  - JOUR
A1  - Vollbrecht, Joachim
A1  - Tokmoldin, Nurlan
A1  - Sun, Bowen
A1  - Brus, Viktor V.
A1  - Shoaee, Safa
A1  - Neher, Dieter
T1  - Determination of the charge carrier density in organic solar cells
BT  - a tutorial
JF  - Journal of applied physics
N2  - The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researchers. Published under an exclusive license by AIP Publishing.
KW  - Electrical properties and parameters
KW  - Organic semiconductors
KW  - Solar cells
KW  - Photoconductivity
KW  - Capacitance spectroscopy
Y1  - 2022
U6  - https://doi.org/10.1063/5.0094955
SN  - 0021-8979
SN  - 1089-7550
SN  - 1520-8850
VL  - 131
IS  - 22
PB  - American Institute of Physics
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Hofmann, Alexander J. L.
A1  - Züfle, Simon
A1  - Shimizu, Kohei
A1  - Schmid, Markus
A1  - Wessels, Vivien
A1  - Jäger, Lars
A1  - Altazin, Stephane
A1  - Ikegami, Keitaro
A1  - Khan, Motiur Rahman
A1  - Neher, Dieter
A1  - Ishii, Hisao
A1  - Ruhstaller, Beat
A1  - Brütting, Wolfgang
T1  - Dipolar Doping of Organic Semiconductors to Enhance Carrier Injection
JF  - Physical review applied
N2  - If not oriented perfectly isotropically, the strong dipole moment of polar organic semiconductor materials such as tris-(8-hydroxyquinolate)aluminum (Alq3) will lead to the buildup of a giant surface potential (GSP) and thus to a macroscopic dielectric polarization of the organic film. Despite this having been a known fact for years, the implications of such high potentials within an organic layer stack have only been studied recently. In this work, the influence of the GSP on hole injection into organic layers is investigated. Therefore, we apply a concept called dipolar doping to devices consisting of the prototypical organic materials N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as nonpolar host and Alq3 as dipolar dopant with different mixing ratios to tune the GSP. The mixtures are investigated in single-layer monopolar devices as well as bilayer metal/insulator/semiconductor structures. Characterization is done electrically using current-voltage (I-V) characteristics, impedance spectroscopy, and charge extraction by linearly increasing voltage and time of flight, as well as with ultraviolet photoelectron spectroscopy. We find a maximum in device performance for moderate to low doping concentrations of the polar species in the host. The observed behavior can be described on the basis of the Schottky effect for image-force barrier lowering, if the changes in the interface dipole, the carrier mobility, and the GSP induced by dipolar doping are taken into account.
KW  - Carrier dynamics
KW  - Electric polarization
KW  - Optoelectronics
KW  - Organic electronics
KW  - Doped semiconductors
KW  - Interfaces
KW  - Organic LEDs
KW  - Organic semiconductors
Y1  - 2019
U6  - https://doi.org/10.1103/PhysRevApplied.12.064052
SN  - 2331-7019
VL  - 12
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  -