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The role of surface passivation for efficient and photostable PbS quantum dot solar cells

Abstract

For any emerging photovoltaic technology to become commercially relevant, both its power conversion efficiency and photostability are key parameters to be fulfilled. Colloidal quantum dot solar cells are a solution-processed, low-cost technology that has reached an efficiency of about 9% by judiciously controlling the surface of the quantum dots to enable surface passivation and tune energy levels. However, the role of the quantum dot surface on the stability of these solar cells has remained elusive. Here we report on highly efficient and photostable quantum dot solar cells with efficiencies of 9.6% (and independently certificated values of 8.7%). As a result of optimized surface passivation and the suppression of hydroxyl ligands—which are found to be detrimental for both efficiency and photostability—the efficiency remains within 80% of its initial value after 1,000 h of continuous illumination at AM1.5G. Our findings provide insights into the role of the quantum dot surface in both the stability and efficiency of quantum dot solar cells.

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Figure 1: Surface of PbS QDs and performance of QD solar cells.
Figure 2: XPS of non-annealed and 80 C-annealed QD layers processed with EDT and TBAI.
Figure 3: EMII-processed PbS QD solar cells.
Figure 4: Photostability assessment of QD solar cells.

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Acknowledgements

The research leading to these results has received funding from Fundació Privada Cellex, and European Community’s Seventh Framework Programme (FP7-ENERGY.2012.10.2.1) under grant agreement 308997. We also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER) through grant MAT2014-56210-R, as well as the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0522). This work was also supported by AGAUR under the SGR grant (2014SGR1548). The authors thank N. C. Miller for optical model simulation and measurement assistance, H. Mäckel for providing the TPC/TPV set-up and Q. Liu for measurement assistance.

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Contributions

G.K. supervised the study. Y.C. and G.K. designed and directed this study and co-wrote the manuscript with feedback from all co-authors. Y.C. fabricated solar cells, characterized their photovoltaic performance, performed ageing tests under AM1.5G illumination, and analysed the XPS and UPS of QD solids. A.S. performed FIB imaging, synthesized colloidal PbS QDs, fabricated and characterized solar cells, and analysed the XPS results. T.L. synthesized colloidal PbS QDs. D.S. performed FET measurements.

Corresponding author

Correspondence to Gerasimos Konstantatos.

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The authors declare no competing financial interests.

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Supplementary Information

Supplementary Figures 1–20, Supplementary Tables 1–7, Supplementary References. (PDF 1519 kb)

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Cao, Y., Stavrinadis, A., Lasanta, T. et al. The role of surface passivation for efficient and photostable PbS quantum dot solar cells. Nat Energy 1, 16035 (2016). https://doi.org/10.1038/nenergy.2016.35

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