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168 Multifunctional Photocatalytic Materials for Energy

Fig. 8.12 (A) Schematic representation of the device architecture of a typical SnO 2 -ETM-
based PSC; (B, C, and D) corresponding energy diagrams of the ITO/SnO 2 /CH 3 NH 3 PbI 3 /
spiroOMeTAD/Ag cells, cross-sectional SEM image, and J-V curves measured under 100 mW/
−2
cm AM 1.5G illumination and in the dark, respectively.
Reprinted with permission from J. Song et al., Low-temperature SnO2-based electron selective
contact for efficient and stable perovskite solar cells. J. Mater. Chem. A 3 (2015) 10837–10844.

indicating that low-temperature-processed SnO 2 with excellent optical and electrical
properties is an excellent alternative ETM for efficient PSCs. Although SnO 2 ETM
layers have shown great potential for application in efficient planar PSCs, in this con-
text, to enhance the interfacial property of SnO 2 -based planar PSC devices, Baena
et al. introduced a low-temperature atomic layer deposition (ALD) technique to ac-
curately deposit an ultrathin (~15 nm) SnO 2 ETM layer [56]. Additionally, the author
fabricated the mixed (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 perovskite material on an SnO 2 ETM
layer to construct a barrier-free band alignment between the perovskite light harvester
and the charge selective contact. In this way, a hysteresis-free planar PSC with a volt-
age as high as 1.19 V was achieved. Interestingly, compared with TiO 2 -based PSC
devices, ALD-SnO 2 -based planar PSCs demonstrated much higher stability in effi-
ciency and negligible hysteresis behavior during an I-V scan. Besides ZnO, TiO 2 , and
SnO 2 , a Lanthanum (La)-doped BaSnO 3 (LBSO) electrode was also employed as an
ETM layer for high photostable PSCs. As is known, LBSO is limited to use in PSCs
because it is difficult to synthesize its highly dispersible, fine crystallized particles
when the temperature is below 500°C. Recently, Seong Sik Shin et al. reported for