Carbazole Derivative Doped Polyoxometalate Inorganic Clusters as Hole Transport Layer to Enhance the Photovoltaic Performance of Organic Solar Cells

Polyoxometalate inorganic clusters (PICs) as a kind of environmentally friendly material can potentially act as an effective hole transport layer (HTL) in organic solar cells (OSCs) due to their thermally stable, low-cost, easily soluble, and excellent redox properties. However, their low conductivity often limits the applications in high-efficiency OSCs. Here, we use a carbazole derivative (2PACz) to modify the bivalent tin (Sn²⁺) doped phosphomolybdic acid (H₃PMo₁₂O₄₀) (termed HPMO-Sn) to further increase the conductivity. The resulted HPMO-Sn:2PACz HTL displays an improved hole transport ability, enhanced conductivity, increased exciton dissociation efficiency, and low nonradiative energy loss in OSCs. As a result, OSCs employing HPMO-Sn:2PACz as the HTL and PM6:Y6 as the active layer exhibit higher power conversion efficiency (17.62%) than those using HPMO-Sn (efficiency: 16.40%) or PEDOT:PSS (efficiency: 16.45%) as the HTL with enhanced open-circuit voltage and fill factor. Our results provide an effective method to elevate the conductivity of PICs and demonstrate the possibility of using the modified PICs as an effective HTL to achieve high-efficiency OSCs.