Doping in OVPD

Research on organic semiconductor materials has resulted in remarkable progress and the introduction of material combinations using hosts and single or multiple guests or additional host materials [24-30]. This demand for simultaneous coevaporation or doping is often difficult to achieve in VTE, but easily achieved by OVPD. In the previous section we explained the OVPD process conditions essen- 

Almost linear OVPD calibration curves of the typical dopant rubrene for a variety of source flows up to 10 seem and up to 50 seem are presented in Fig. 9.9, which shows that the deposition rate can be precisely adjusted from 0.06 to 1.6 A s-1. Both curves are an ideal fit and reveal a linear relationship between deposition rate and source flow they were collected with two mass-flow controllers of different capacity ranges (10 seem and 50 seem). Ellipsometric thickness analysis confirmed for both experiments a deposition rate of 0.3564 and 0.3582 A s-1, which is a relative error of only 0.48% and is identical with our prediction of dopant controllability (Table 9.1). Using a standard OVPD deposition rate of 10 A s-1 for a hosts the doping range of rubrene can be very precisely adjusted in the range of 0-16%. 

Consequently, this straightforward realization of vertical doping profiles and material mixtures enables precise layer fine-tuning to optimize device performance, for example power efficiency or lifetime [25]. For current OLED research and development and production [32, 33] doping and coevaporation are fundamental for device optimization and longer lifetimes. 

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