Screen printed carbon CsPbBr3 solar cells with high open-circuit photovoltage

Screen printed mesoporous carbon solar cells (mC-PSC) are a promising fully printable technology that does not require organic hole conductors, expensive metal contacts or vacuum processing. However, when infiltrated with the archetypal CH3NH3PbI3 perovskite, mC-PSCs show low voltage which limits their use in innovative applications such as indoor light harvesting. Here we investigate both planar (C-PSC) and mesoporous (mC-PSC) carbon cells, based on all-inorganic CsPbBr3. Pure CsPbBr3 is a yellow material with an orthorhombic crystal structure at room temperature and a 2.3 eV band gap, which is not ideal for solar cell applications. However, CsPbBr3 is thermally stable up to over 400 degrees C and high-voltage planar carbon solar cells, with open circuit voltages of up to 1.29 V and efficiencies up to 6.7% have been reported in the literature. We focus on the effect of the post-annealing temperature on the material properties and photovoltaic activity. XPS and XRD results show a non-linear trend with temperature, with significant improvements in composition between 200 and 300 degrees C. Both the mesoporous and planar champion devices were obtained after heat processing at 400 degrees C, reaching PCEs of 8.2% and 5.7% respectively. The average V-oc for the planar and mesoporous devices were 1.33 V and 1.27 V respectively with a record 1.44 V for the best mC-PSC.