Work Function TunedSolution Processable Graphene Derivatives as Buffer Layers for High Efficient Organic and Perovskite Solar Cells

Dimitrios Konios^a, George Kakavelakis^a, Emmanuel Kymakis^a, Costas Petridis^a, Emmanuel Stratakis^b

^aTechnological Educational Institute of Crete, Center of Materials Technology & Photonics, Estavromenos P.B 1939, Heraklion, Greece

^bInstitute of Electronic Structure and Laser (IESL) Foundation for Research and Technology-Hellas (FORTH), Heraklion, GR-711 10, Crete, Greece

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)

Swansea, United Kingdom, 2016 June 29th - July 1st

Organizers: James Durrant, Henry Snaith and David Worsley

Oral, George Kakavelakis, presentation 083
Publication date: 28th March 2016

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 TiO₂ ETM, enabling excellent electron transport for both PV devices. The utilization of these graphene-based HT and ETM in PTB7:PC₇₁BM 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(~12%) 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.

[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

Acknowledgment: The research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement no 604391 Graphene Flagship.

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