The sensitive devices are multilayer stacked structures p-i-n/p-i-n based on a-SiC:H and a-Si:H between two transparent conductive contacts. The thickness and the absorption coefficient of the front p-i-n cell is optimized for blue collection and red transmittance and the thickness of the back one adjusted to achieve full absorption in the green and high collection in the red spectral ranges. Color discrimination is achieved through the modulation of one, two or both cell depletion regions by an applied external voltage. The devices are characterized through the analysis of the photocurrent and spectral response under different steady state optical bias and applied voltages. In order to achieve full color discrimination and to evaluate the sensors responsivity to different light wavelengths, the photocurrent generated by a modulated red light is measured under different optical/electric bias. The sensor element is illuminated through the back diode with red modulated light and the optical bias applied onto the front diode. From the experimental-results it is observed that when using a red modulated light the thin a-SiC: H front absorber (200 run) maximizes the conversion efficiency for blue front optical bias and the thickest back absorber layer (1000 nm) minimizes the conversion efficiency in the red range. Results show that the conversion efficiency to a red modulated light under blue front optical bias is maximized when a 200 nm a-SiC: H front absorber is used, and minimized in the red range if the absorber layer of the back diode is around 1000 nm thick. In those devices the green photons absorption occurs mainly across the front diode, the n-p defectous interface and at the front side of the back diode. Under reverse bias and blue irradiation the collection is high since the back diode becomes fully depleted due to its self-biasing process. Under red illumination the aSi:H back absorber acts as a load due to the high light penetration depth of the red photons and the low collection is determined by the dark characteristics of the front diode. In the green spectral range the reverse bias increases the potential drop across the back diode and the collection increases linearly. The effect of the applied voltage on the color selectivity and spectral sensitivity is discussed and supported by a physical model based on a numerical simulation. (c) 2005 Elsevier B.V. All rights reserved.