Method of forming polycrystalline silicon layer, and thin film transistor and organic light emitting device including the polycrystalline silicon layer

A thin film transistor comprising:

• a polycrystalline silicon layer that is crystallized using a metal catalyst;
• a gate electrode overlapping with the polycrystalline silicon layer;
• and
• a source electrode and a drain electrode electrically connected with the polycrystalline silicon layer,
• wherein the polycrystalline silicon layer includes a first polycrystalline silicon layer and a second polycrystalline silicon layer having different grain sizes from each other.

An organic light emitting device comprising:

• a thin film transistor including a gate electrode, a polycrystalline silicon layer that overlaps with the gate electrode and is crystallized using a metal catalyst, and a source electrode and a drain electrode opposite each other with the polycrystalline silicon layer as the center;
• a first electrode electrically connected with the thin film transistor;
• a second electrode opposite to the first electrode;
• and
• an emission layer positioned between the first electrode and the second electrode, wherein the polycrystalline silicon layer includes a first polycrystalline silicon layer and a second polycrystalline silicon layer having different grain sizes from each other.