## 2 Materials and Methods  
### Design of DBR for OLEDs  
Zirconium oxide (ZrO\({}_{2}\)) and zircone were used as the bottom dielectric mirror for the DBR structure. In OLED devices, molybdenum oxide (MoO\({}_{3}\)) and 1,4-bis[N-(1-naphthyl)-N0-phenylamino]-4,4\({}^{\prime}\) diamine (NPB) are employed as hole injection layers (HIL); 4,4\({}^{\prime}\),4\({}^{\prime\prime}\)-tris-(N-carbazolyl)-triphenylamine (TCTA) is employed as a hole transport layer (HTL); lithium fluoride (LiF) is the electron injection layer (EIL); tris(8-hydroxyquinoline) aluminum (Alq\({}_{3}\)) and 1,3,5-tris(2N-phenylbenzimidazolyl)benzene (TPBi) are electron transport layers (ETL). The emitting layer (EML) in Device A is composed of two emission components: TCTA doped with 10 wt% of fac-tris(2-phenylpyridine) iridium (Ir(ppy)\({}_{3}\)) acts as a green-emitting material layer (EML), while 3 wt% 1-4-Di-[4-(N,\(N\)-diphenyl)amino]styryl-benzene (DSA-Ph)-doped 4,4\({}^{\prime}\)-bis(N-carbazolyl)biphenyl1 (CBP) acts as a blue EML.  
Figure 1 displays the schematic structure of the device with the DBR. In OLEDs, a metal cathode and dielectric mirror were formed together on the glass substrate, which defined the microcavity  
structure. The aluminum (Al) metal layer and six pairs of the ZrO\({}_{2}\)/zircone stack were used as cathode and DBR layers. A classical calculation was performed to estimate the dielectric mirror regarding its reflectivity through refractive indices. In Figure 1, the numbers in parentheses after zircone (1.46) and ZrO\({}_{2}\) (2.1) are refractive indices. The light generated in OLEDs was emitted through the dielectric mirror as well as the glass substrate. The equation below helped to calculate the forward theoretic emission spectrum considering the classical optics [19].  
\[E_{cap}(\lambda)^{2}=\frac{(1-R_{d})[1+R_{m}+2R_{m}^{0.5}\cos(\frac{4\pi\chi}{ \lambda})]}{1+R_{d}R_{m}-2(R_{d}R_{m})^{0.5}\cos(\frac{4\pi\chi}{\lambda})}E_{ n}(\lambda)^{2}\]  
where \(\lambda\) denotes the wavelength of emission, \(x\) denotes the emitting layer's effective distance between the metal mirror, and indium-tin oxide (ITO) substrate, \(R_{m}\) represents the reflectivity exhibited by the metal mirror, and \(R_{d}\) represents the reflectivity exhibited by the dielectric mirror. \(L\) denotes the overall optical length exhibited by the microcavity OLED device. \(E_{n}(\lambda)\) denotes the original spectrum. The below equation expresses \(L\) considering the classical optics [20].  
\[L=\frac{\lambda}{2}(\frac{n_{eff}}{\Delta n})+\sum\
olimits_{i}n_{i}d_{i}+ \left|\frac{\phi_{m}}{4\pi}\lambda\right|\]  
where \(n_{eff}\) stands for the essential index of refraction, \(\Delta n\) stands for the difference in the index of refraction between the two layers of the dielectric mirror, \(d_{i}\) stands for the thickness, and \(n_{i}\) stands for the index of refraction exhibited by the organic layers as well as ITO. \(\Phi_{m}\) refers to the change in phase at the metal mirror. The relationship \(m\lambda=2L(\lambda)\) expresses the cavity mode, where \(m\) denotes the index of the mode, where the adjustment can be performed via changing the length of the cavity, i.e., \(L(\lambda)\).