ZnO electron transporting layer engineering realized over 20% efficiency and over 1.28 V open-circuit voltage in all-inorganic perovskite solar cells

Cesium lead based all-inorganic perovskite solar cells (PSCs) are promising candidates for tandem solar cells owing to their favorable thermal stability and suitable bandgap. However, to exploit the advantage to the full, there is still huge room to reduce energy loss and enhance the V-OC. In this work, we developed low-temperature processed ZnO as an ETL alternative. Incorporation of PbX2 (X = I-, Cl-, and CH3COO-) was found to increase oxygen vacancies in ZnO, which not only promoted the growth of all-inorganic perovskite layer with improved morphology and orientational order, but also formed a favorable energy level alignment with the perovskite layer, thus facilitating charge extraction and suppressing charge recombination. Consequently, the CsPb(I1-xBrx)(3) PSCs based on PbX2:ZnO exhibited enhanced stability and performance. The efficiency was boosted from 17.64% to 20.04% with an improved fill factor of 84.14% and a V-OC of 1.28 V, being the highest V-OC among highly efficient (>20%) all-inorganic PSCs to date.