Tuning surface chemistry and morphology of graphene oxide by γ-ray irradiation for improved performance of perovskite photovoltaics

We demonstrated a simple and effective modification of graphene oxide (GO) to enhance the device performance of perovskite photovoltaics. The surface chemistry and morphology of GO was tailored by irradiating aqueous GO solution with ⁶⁰Co γ-ray. During the irradiation, hydroxyl radicals were believed to be released from water radiolysis and oxidized the surface of pristine GO sheets, supposedly. Furthermore, large GO agglomerates scattered as individual GO sheets with small lateral dimensions, which is advantageous to uniform distribution of GO sheets in PEDOT:PSS layer. PEDOT:PSS layer with γ-ray irradiated GO (γ-GO) facilitated efficient hole transport properties in perovskite solar cells. PEDOT:PSS layer became more hydrophobic by embedding γ-GO after thermal annealing and thus improved the crystallinity of perovskite layer on top of the PEDOT:PSS. Consequently, embedding γ-GO in PEDOT:PSS layer resulted in better electrical properties than PEDOT:PSS layer without GO or with pristine GO. As a result, power conversion efficiency was improved owing to increased charge generation/extraction, and photoluminescence in the perovskite photoactive layer.