Role of the electronically-active amorphous state in low-temperature processed In2O3 thin-film transistors†
Metal oxide (MO) thin-film transistors (TFTs) are expected to enable low-cost flexible and printed electronics, given their excellent charge transport, low processing temperatures and solution processability. However, achieving adequate mobility when processed scalably at low temperatures compatible with plastic electronics is a challenge. Here, we explore process-structure-transport relationships in blade-coated indium oxide (In2O3) TFTs via both sol–gel and combustion chemistries. We find that the sol–gel chemistry enables n-type TFTs when annealed at 200 °C to 225 °C with noticeable electron mobility ((3.4 ± 0.4) cm2 V−1 s−1) yet minimal In2O3 crystallinity and surprisingly low levels of the metal–oxygen–metal (M–O–M) lattice content (≈46%). Increased annealing temperatures result in the appearance of nanocrystalline domains and an increase in M–O–M content to ≈70%, without any further increase in mobility. An acetylacetone combustion-assisted ink lowers the external thermal budget required for In2O3 crystallization but bypasses the electronically-active amorphous state and underperforms the sol–gel ink at low temperatures. Grain boundary formation and nanocrystalline inclusions in these films due to rapid combustion-assisted crystallization are suggested to be the likely origin behind the significantly compromised charge transport at low-temperatures. Overall, this study emphasizes the need to understand the complex interplay between local order (nanocrystallinity) and connectivity (grain boundary, amorphous phases) when optimizing low-temperature processed MO thin films.