Effect of guanidinium chloride in eliminating O 2 − electron extraction barrier on a SnO 2 surface to enhance the efficiency of perovskite solar cells

/perovskite interface due to the strong coupling between the GA and the adsorbed oxygen, which has been supported by the FTIR and XPS results. The strategy of reducing the charge extraction barrier by GA modification has been demonstrated to be an efficient approach to improve both the PCE and stability.