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  - Ran, Niva A.
A1  - Love, John A.
A1  - Heiber, Michael C.
A1  - Jiao, Xuechen
A1  - Hughes, Michael P.
A1  - Karki, Akchheta
A1  - Wang, Ming
A1  - Brus, Viktor V.
A1  - Wang, Hengbin
A1  - Neher, Dieter
A1  - Ade, Harald
A1  - Bazan, Guillermo C.
A1  - Thuc-Quyen Nguyen, 
T1  - Charge generation and recombination in an organic solar cell with low energetic offsets
JF  - dvanced energy materials
N2  - Organic bulk heterojunction (BHJ) solar cells require energetic offsets between the donor and acceptor to obtain high short-circuit currents (J(SC)) and fill factors (FF). However, it is necessary to reduce the energetic offsets to achieve high open-circuit voltages (V-OC). Recently, reports have highlighted BHJ blends that are pushing at the accepted limits of energetic offsets necessary for high efficiency. Unfortunately, most of these BHJs have modest FF values. How the energetic offset impacts the solar cell characteristics thus remains poorly understood. Here, a comprehensive characterization of the losses in a polymer:fullerene BHJ blend, PIPCP:phenyl-C61-butyric acid methyl ester (PC61BM), that achieves a high V-OC (0.9 V) with very low energy losses (E-loss = 0.52 eV) from the energy of absorbed photons, a respectable J(SC) (13 mA cm(-2)), but a limited FF (54%) is reported. Despite the low energetic offset, the system does not suffer from field-dependent generation and instead it is characterized by very fast nongeminate recombination and the presence of shallow traps. The charge-carrier losses are attributed to suboptimal morphology due to high miscibility between PIPCP and PC61BM. These results hold promise that given the appropriate morphology, the J(SC), V-OC, and FF can all be improved, even with very low energetic offsets.
KW  - energetic offset
KW  - fill factor
KW  - morphology
KW  - organic solar cells
KW  - recombination
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201701073
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 5
PB  - Wiley-VCH
CY  - Weinheim
ER  -