Influence of Carrier Density and Energy Barrier Scattering on a High Seebeck Coefficient and Power Factor in Transparent Thermoelectric Copper Iodide
Peter P. Murmu, V. Karthik, Zihang Liu, Vedran Jovic, Takao Mori, Wanli Yang, Kevin E. Smith, J. Kennedy
Abstract
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 2p3/2 spectrum, which suggested the presence of Cu0-like defect states in γ-CuI films. Interface and grain boundaries of CuI and Cu0 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 (α2σ = 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 (Tvisible ∼ 60–85%) γ-CuI films for energy harvesting as smart windows.