Work function tuned solution processable graphene derivatives as buffer layers for high
efficient organic and perovskite solar cells
George Kakavelakis
1,*
, Dimitrios Konios
1
, Costas Petridis
1
, Emmanuel Stratakis
2
and Emmanuel Kymakis
1
1
Center of Materials Technology & Photonics and Electrical Engineering Department,
Technological Educational Institute (TEI) of Crete, Heraklion, Greece
2
Institute of Electronic Structure and Laser (IESL) Foundation for Research and
Technology-Hellas (FORTH), Heraklion , Greece
E-mail:
The effective utilization of work-function (WF) tuned solution processable graphene-
based derivatives as hole and electron transport materials (HTM and ETM) in organic
photovoltaics (OPV) and perovskite solar cells (PeSCs) is demonstrated.
The systematic tuning of the functionalized graphene oxide (GO) WF took place by
either photochlorination for WF increase, or alkali metal neutralization for WF decrease.
1,2
In
this way, the WF of the photochlorinated GO (5.23 eV) layer was perfectly matched with the
HOMO level of two different polymer donors, enabling excellent hole transport in OPV
devices. Meanwhile the WF of the lithium functionalized GO (4.3 eV) was perfectly
matched with the LUMO level of the fullerene acceptor, and TiO
2
ETM, enabling excellent
electron transport for both PV devices. The utilization of these graphene-based HT and ETM
in PTB7:PC
71
BM active layer devices led to
∼
19% enhancement in the power conversion
efficiency (PCE) compared to that of the reference graphene free device, resulting in the
highest reported PCE for graphene-based buffer layer OPVs of 9.14%.
3
On the other hand,
the utilization of GO-Li ETM in perovskite solar cells in both mesoporous and planar
inverted structures lead to a significant enhancement of the electron injection from the
perovskite to the respective electrode due to the good energy matching with the conduction
band of the perovskite, improving in this way the device efficiency and stability and
simultaneously decreasing the hysteresis.
4
Finally, the incorporation of a thin layer of
potassium neutralized GO (GO-K) as an interfacial hole blocking layer, resulted in a
significant decrease of the charge carrier recombination due to its low WF value (3.6 eV).
The charge trap density was reduced, significantly improving the transport and collection of
photogenerated charges, which in turn improved the device efficiency.
Acknowledgment: The research leading to these results has received funding from the
European Union Seventh Framework Programme under grant agreement no 604391
Graphene Flagship.
1
Stratakis E., Savva K., Konios D., Petridis C., Kymakis E., (2014),
Nanoscale
, 6, 6925-
6931
2
Kakavelakis G., Konios D., Stratakis E., Kymakis E., (2014),
Chemistry of Materials
, 26
(20), 5988–5993
3
Konios D., Kakavelakis G., Petridis C., Stratakis E., Kymakis E., (2016)
Journal of
Materials Chemistry A
, 4, 1612-1623
4
Agresti A., Pescetelli S.,Cina L., Konios D., Kakavelakis G., Kymakis E., Di Carlo A.,
(2016),
Advanced Funtional Materials
, DOI: 10.1002/adfm.201504949
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