TY  - JOUR
A1  - Armin, Ardalan
A1  - Chen, Zhiming
A1  - Jin, Yaocheng
A1  - Zhang, Kai
A1  - Huang, Fei
A1  - Shoaee, Safa
T1  - A Shockley-Type polymer
BT  - Fullerene solar cell
JF  - Advanced energy materials
N2  - Charge extraction rate in solar cells made of blends of electron donating/accepting organic semiconductors is typically slow due to their low charge carrier mobility. This sets a limit on the active layer thickness and has hindered the industrialization of organic solar cells (OSCs). Herein, charge transport and recombination properties of an efficient polymer (NT812):fullerene blend are investigated. This system delivers power conversion efficiency of >9% even when the junction thickness is as large as 800 nm. Experimental results indicate that this material system exhibits exceptionally low bimolecular recombination constant, 800 times smaller than the diffusion-controlled electron and hole encounter rate. Comparing theoretical results based on a recently introduced modified Shockley model for fill factor, and experiments, clarifies that charge collection is nearly ideal in these solar cells even when the thickness is several hundreds of nanometer. This is the first realization of high-efficiency Shockley-type organic solar cells with junction thicknesses suitable for scaling up.
KW  - charge transport
KW  - non-Langevin recombination
KW  - organic solar cells
KW  - thick junctions
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201701450
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 7
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Shoaee, Safa
A1  - Armin, Ardalan
A1  - Stolterfoht, Martin
A1  - Hosseini, Seyed Mehrdad
A1  - Kurpiers, Jona
A1  - Neher, Dieter
T1  - Decoding Charge Recombination through Charge Generation in Organic Solar Cells
JF  - Solar RRL
N2  - The in-depth understanding of charge carrier photogeneration and recombination mechanisms in organic solar cells is still an ongoing effort. In donor:acceptor (bulk) heterojunction organic solar cells, charge photogeneration and recombination are inter-related via the kinetics of charge transfer states-being singlet or triplet states. Although high-charge-photogeneration quantum yields are achieved in many donor:acceptor systems, only very few systems show significantly reduced bimolecular recombination relative to the rate of free carrier encounters, in low-mobility systems. This is a serious limitation for the industrialization of organic solar cells, in particular when aiming at thick active layers. Herein, a meta-analysis of the device performance of numerous bulk heterojunction organic solar cells is presented for which field-dependent photogeneration, charge carrier mobility, and fill factor are determined. Herein, a "spin-related factor" that is dependent on the ratio of back electron transfer of the triplet charge transfer (CT) states to the decay rate of the singlet CT states is introduced. It is shown that this factor links the recombination reduction factor to charge-generation efficiency. As a consequence, it is only in the systems with very efficient charge generation and very fast CT dissociation that free carrier recombination is strongly suppressed, regardless of the spin-related factor.
KW  - charge generation
KW  - charge transfers
KW  - non-Langevin recombination
KW  - spin-related factors
Y1  - 2019
U6  - https://doi.org/10.1002/solr.201900184
SN  - 2367-198X
VL  - 3
IS  - 11
PB  - Wiley-VCH
CY  - Weinheim
ER  -