Design tungsten oxides hole transport layers (HTLs) to modify the back interface in all-inorganic carbon-based CsPbBr3 solar cells

To enhance the inferior photovoltaic performance of all-inorganic carbon-based perovskite solar cells (C-PSCs) caused by inefficient charge extraction and transport processes of the CsPbBr 3 /carbon back interface, three types of tungsten oxides (WO 3 , WO 2.72 , WO 2 ) are synthesized as low cost and stable hole transport layers (HTLs) to modify the back interface by tunning the energy level alignment. Among the three kinds of tungsten oxides, WO 3 shows the best hole extraction and transport capability and the C-PSCs using WO 3 HTL generates a power conversion efficiency (PCE) of 7.90% with a high open circuit voltage (V oc ) of 1.307 V, indicating a great PCE enhancement of 43.9%, as compared with the device without HTL (5.49%). Meanwhile, WO 2.72 and WO 2 also are also proved to be qualified HTLs and the devices show PCE values of 7.57% and 6.24%, respectively. Importantly, WO 3 and WO 2.72 based device show excellent stabilities with PCE retention over 90% of the initial PCE values under ambient conditions for 60 days.