Over the past few years single junction perovskite solar cells have been extensively studied with reported power conversion efficiencies approaching 20% [1-3]. Despite such advances, high efficiency combined with low fabrication cost, parasitic absorptions and long term stability have remained issues. One approach to curtail some of these obstacles has been the investigation of planar architectures where the mesoporous TiO₂/Al₂O₃ is removed from the cell and the electron transport layer (ETL) is reduced to a nanometre scale compact charge blocking layer [4]. Typically this layer has been TiO₂ but more recently band gap engineering studies have shown that SnO₂ has significant potential in removing TiO₂ hysteresis effects whilst maintaining efficiencies [5]

In this study we examined planar stacks comprising glass/FTO/ETL/perovskite/spiro MeOTAD hole transport layer/contacts with an aim to further optimize the metal oxide ETL. The metal oxides studied in this work were atomic layer deposition grown SnO₂, nominally undoped TiO₂ and doped TiO_2, all grown at temperatures below 180°C to align with the requirements of silicon-perovskite heterojunction cells [6]. The influence of the ALD growth parameters and composition of the ETL on the subsequent perovskite deposition, as well as the resultant cell performance are highlighted and discussed in terms of efficiency and hysteresis.

1. W.S. Yang et al., Science, 348, 1234-1237 (2015).
2. N.J. Jeon et al., Nature, 517, 476- 480, (2015).
3. S.D. Stranks et al., Science 342, 341-344, (2013)
4. M. Liu et al., Nature, 501, 395- 398, (2013).
5. J.P. Correa Baena, Energy and Environment Science, DOI:10.1039/c5ee02608c, (2015).
6. J.P. Mailoa et al., Applied Physics Letters, 106, 121105 (2015).