Fig. 3: Mechanisms inducing NCPE or ACPE.
From: Electrical control of photon spin angular momentum in organic electroluminescent materials

a, NCPE occurs when there is balanced charge transport in the device through the omission of an HTL. b,c, ACPE occurs when charge transport is unbalanced towards electron transport through the addition of an HTL. For conventional devices, the RZ is close to the front electrode (b), whereas for inverted devices, the RZ is close to the back electrode (c). The positioning of the RZ controls the handedness of the ACPE through oppositely induced OAM.