Extending the environmental lifetime of unpackaged perovskite solar cells through interfacial design

Solution-processed oxo-functionalized graphene (oxo-G(1)) is employed to substitute hydrophilic PEDOT:PSS as an anode interfacial layer for perovskite solar cells. The resulting devices exhibit a reasonably high power conversion efficiency (PCE) of 15.2% in the planar inverted architecture with oxo-G(1) as a hole transporting material (HTM), and most importantly, deploy the full open-circuit voltage (V-oc) of up to 1.1 V. Moreover, oxo-G(1) effectively slows down the ingress of water vapor into the device stack resulting in significantly enhanced environmental stability of unpackaged cells under illumination with 80% of the initial PCE being reached after 500 h. Without encapsulation, similar to 60% of the initial PCE is retained after similar to 1000 h of light soaking under 0.5 sun and ambient conditions maintaining the temperature beneath 30 degrees C. Moreover, the unsealed perovskite device retains 92% of its initial PCE after about 1900 h under ambient conditions and in the dark. Our results underpin that controlling water diffusion into perovskite cells through advanced interface engineering is a crucial step towards prolonged environmental stability.