Solution-Processed Bi2S3 Passivation Layers for CH3NH3PbX3 (X = Cl, Br, I) Perovskite Solar Cells

Christine Buchmaier^a, Gregor Trimmel^a, Indira Zahirovic^a, Thomas Rath^a, Ferdinand Hofer^b, Angelika Reichmann^b, Birgit Kunert^c, Roland Resel^c

^aGraz University of Technology, Institute for Chemistry and Technology of Materials (ICTM), NAWI, Stremayrgasse, 9, Graz, Austria

^bInstitute for Electron Microscopy and Fine Structure Research, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria

^cInstitute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria

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

Poster, Christine Buchmaier, 288
Publication date: 28th March 2016

Perovskites have been confirmed as a promising material for thin film photovoltaics, as they combine high power conversion efficiency with low cost processing. In order to make them marketable, efforts are required to increase their long term stability. This also includes the investigation of the interfaces within the device regarding their influence on power conversion efficiency and device stability. In the commonly used TiO₂ electron transport layer, intrinsic defects such as oxygen vacancies and titanium interstitials can occur, which leads to detrimental deep trap states, and thus to the reduction of the solar cell performance. ^[1]

Pathak et al. ^[2] demonstrated the positive effect of aluminum-doped TiO₂ layers on device performance and stability due to the passivation of these detrimental intrinsic defects. Ito et al. ^[3] could also improve the stability of perovskite solar cells against light irradiation by introducing a Sb₂S₃ layer between the TiO₂ and the perovskite absorber layer, which caused a passivation of the TiO₂ photocatalytic effect. Moreover, the Sb₂S₃ layer led to a spike-like conduction band offset, inducing higher photo energy conversion efficiencies.

The environmentally friendly Bi₂S₃ has similar valence and conduction band edges to that of Sb₂S₃. Therefore we investigated the effects of a thin Bi₂S₃ passivation layer on the stability and the performance of CH₃NH₃PbX₃ perovskite solar cells. The passivation layer was inserted at the interface between the electron transport and the perovskite absorber layer, using two different solution-based approaches. In the first approach thin Bi₂S₃ layers were deposited via chemical bath deposition and in the second approach bismuth dithiocarbonates were used as single source precursors. The Bi₂S₃ passivation and the perovskite absorber layers were characterized in terms of roughness, crystallinity, chemical composition, purity and morphology by surface profilometry, X-ray diffraction and scanning electron microscopy. To test their effects on power conversion efficiency and device stability perovskite based solar cells were prepared and characterized by current-voltage and optical measurements.

[1] D. Wang et al., Sol. Energy Mater. Sol. Cells 147 (2016) 255-275.

[2] S. K. Pathak et al., Adv. Funct. Mater. 24 (2014) 6046-6055.

[3] S. Ito et al., J. Phys. Chem. C 118 (2014) 16995-17000.

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