“…In our previous study [1], we showed that in a curved OLED, because the tangential plane of the emitting point, PA, is not parallel to the tangential plane on the light exit surface, PB (between the substrate/superstrate and the air as illustrated in Figure. 2), the initial emission angle, θ1, would not equal to the incident angle, θ2, on PB and hence the effective critical angle, θc,eff (i.e., escape cone), seen by the original emitter would differ from the critical angle, θc, in the planar structure. In spherical convex or cylindrical convex structures as in Figure. 2, θc,eff would be larger than θc, possibly resulting in significant enhancement in light out-coupling with appropriate designs (i.e., >90% substrate-to-air extraction efficiency).…”