(a) Normalized EL spectra of device-W under a bias of 7 V, in which the weight ratio of G:R and the total thickness values of the mixed QDs layers for devices W1, W2, and W3, are 1:5 with 0.51 ML, 1:5 with 0.62 ML, and 1:4 with 0.67 ML respectively. (b) L–V–J and (c) current efficiency–current density of devices-W with upper inset: device structure of the device-W, below-left inset: photo of the 3 mm×3 mm active area emitting device-W3 at 7 V, and below-right inset: photo of 2.1-inch (1 inch = 2.54 cm) white QLED at 8 V.