Full-phosphorescence white organic light-emitting diode with high CRI: the exploitation of positive and reverse emitter sequences

The high color rendering index (CRI) and doping-free four-emitting-layer (EML) white orangic light-emitting diode (WOLED) with bipolar spacer layer was researched by different emitter sequence arrangements (positive emitter sequence: B-G-O-R, reverse emitter sequence: R-O-G-B). The resulting four-emitting-layer WOLEDs with different sequences show opposite CRI trends when voltage increases, which includes the decreased trend in B-G-O-R sequence and increased trend in R-O-G-B sequence. That leads to WOLEDs with different sequences exhibit the highest CRI at obviously distinguishing luminance, which are CRI of 86 @ 531 cd m −2 in B-G-O-R sequence and CRI of 87 @ 13,340 cd m −2 in R-O-G-B sequence, respectively. Meanwhile, the B-G-O-R and R-O-G-B sequences devices also exhibit a difference in the power efficiency. The different manifestations of CRI and effeciency characteristics are meticulously analyzed by a combined operation of energy transfer mechanism, carrier trap effect and the movement of carrier recombination zone in EML, resulting in a meaningful concept to design high CRI WOLEDs in different application scene.