Optical and barrier properties of thin-film encapsulations for transparent OLEDs

We investigate the optical and barrier properties of thin-film encapsulations (TFEs) for transparent organic light-emitting diodes (TOLEDs). To improve the barrier property of OLEDs, the number of dyads (Al₂O₃/polymer) and the thickness of polymer layer in the TFE structure are required to be increased. It is, however, demonstrated that a sharp dip appears in the transmittance of TFE films due to the interference of light caused by organic/inorganic multi-layered configuration, resulting in a dip in the top emission spectrum of TOLEDs. We have found that such a transmittance dip deepens when the number of dyads is large. What is worse, the number of transmittance dips and their sharpness are raised with increased thickness of the polymer layer. When the number of dyads is small, however, the effect of the polymer layer thickness on such a transmittance dip is weak. Therefore, we have addressed that the number of dyads needs to be reduced, but the thickness of the polymer layer should be increased to meet both optical and barrier properties of TOLEDs at the same time.