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.