Transparent thermoelectric materials offer a synergetic performance for energy harvesting as smart windows. Among them, p-type copper iodide (CuI) is preferred due to its low synthesis temperature, moderate conductivity and mobility, and high optical transparency. X-ray absorption spectroscopy results showed a pre-edge feature in the Cu 2p 3/2 spectrum, which suggested the presence of Cu 0 -like defect states in γ-CuI films. Interface and grain boundaries of CuI and Cu 0 act as a potential energy barrier for energy filtering of charge carriers, which along with the decrease in charge carrier density enhanced the Seebeck coefficient, α. The α value increased by 298% upon annealing at 100 °C, α = 789.5 μVK −1 , which resulted in a 480% increase in the power factor (α 2 σ = 740.9 μWm −1 K −2 ). Our results showed that a high Seebeck coefficient resulted from a decrease in charge carrier density and energy filtering of charge carriers at the interface and grain boundaries in optically transparent (T visible ∼ 60−85%) γ-CuI films for energy harvesting as smart windows.

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