Interstitial Doping of SnO₂ Film with Li for Indium-Free Transparent Conductor

SnO₂ films exhibit significant potential as cost-effective and high electron mobility substitutes for In₂O₃ films. In this study, Li is incorporated into the interstitial site of the SnO₂ lattice resulting in an exceptionally low resistivity of 2.028 × 10⁻³ Ω⋅cm along with a high carrier concentration of 1.398 × 10²⁰ cm⁻³ and carrier mobility of 22.02 cm²/V⋅s. Intriguingly, Li_i readily forms in amorphous structures but faces challenges in crystalline formations. Furthermore, it has been experimentally confirmed that Li_i acts as a shallow donor in SnO₂ with an ionization energy ΔE_D1 of −0.4 eV, indicating spontaneous occurrence of Li_i ionization.