Compensators for liquid crystal displays with biaxially stretched single film with crystallization modifier

An optical stack comprising:

• a) a polarizer layer;
• and
• b) a simultaneous biaxally stretched polymeric film, wherein said film is a single layer, said single aver comprising a non-cyclic polyolefin polymer and said single layer has the properties of being substantially non-absorbing and non-scattering for at least one polarization state of visible light, the simultaneous biaxally stretched polymeric film having x, y, and z orthogonal indices of refraction wherein at least two of the orthogonal indices of refraction are not equal, an in-plane retardance being 100 nm or less and an out-of-plane retardance being 50 nm or greater, wherein the simultaneous biaxally stretched polymeric film comprises a crystallization modifier.