High-Resolution Study of TiO₂ Contact Layer Thickness on the Performance of over 800 Perovskite Solar Cells

In this Letter, we systematically explore the influence of TiO₂ thickness with nanometric variations over a range of 20-600 nm on the photovoltaic parameters (open-circuit voltage, short circuit current, fill-factor, and power conversion efficiency) of CH₃NH₃PbI₃-based solar cells. We fabricate several sample libraries of 13 × 13 solar cells on large substrates with spatial variations in the thickness of the TiO₂ layers while maintaining similar properties for the other layers. We show that the optimal thickness is ∼50 nm for maximum performance; thinner layers typically resulted in short-circuited cells, whereas increasing the thickness led to a monotonic decrease in performance. Furthermore, by assuming a fixed bulk resistivity of TiO₂, we were able to correlate the TiO₂ thickness to the series and shunt resistances of the devices and model the variation in the photovoltaic parameters with thickness using the diode equation to gain quantitative insights.