Colour Characterisation of a-Si:H-Based Three-Terminal Three-Channel Detector
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Colour Characterisation of a-Si:H-Based Three-Terminal Three-Channel Detector Janez Krč1, Marko Topič1, Franc Smole1, Dietmar Knipp2 and Helmut Stiebig2 1 Faculty of Electrical Engineering, University of Ljubljana, Slovenia 2 Institut für Photovoltaik, Forschungszentrum Jülich, Germany ABSTRACT Colour characterisation of a three-terminal three-channel colour detector in the assembly glass/TCO1/PI1NI2P/TCO2/PI3N/Al is performed, using a method of polynomial regression. The metameric errors of the detector calculated and investigated for different orders of polynomial colour correction are presented and discussed. The benefits of the first order colour correction are shown and graphically illustrated. The final transformation matrix for the first order colour correction and conversion to the output R, G and B signals is given. At the end, a demonstrational application with the a-Si:H-based detector and corresponding read-out and colour correction electronics is presented. INTRODUCTION Colour detection is one of the basic tasks in all contemporary light-detecting appliances such as computer scanners, cameras and photocopy machines. A conventional approach of colour detection with CFAs (Colour Filter Arrays) enables quite accurate colour determination with low metameric errors [1] but also exhibits an undesirable Moire effect [1], which arises due to areal dislocations of colour filters. In order to avoid the Moire effect, one of the possible substitution of CFAs may present hydrogenated amorphous silicon (a-Si:H)-based Moire-free colour detectors [2-4]. Their vertically stacked structure of a-Si layers with different optical and electrical properties enables selective colour detection of the visible light spectrum in a single areal point without using any additional filter coatings. Since the spectral responses of detectors are generally not exactly matched with the standard observers’ spectral responses (human eye), for accurate colour detection a correction of the detector output signals should be made. For this reason, one of the methods of colour characterisation [1,2] giving an optimal transformation for colour correction of the specific aSi:H-based detector should be performed. In this work we present the colour characterisation using polynomial regression method for an a-Si:H-based three-terminal three-channel detector with smooth boundaries in the assembly glass/TCO1/PI1NI2P/TCO2/PI3N/Al [3,4], where the PI1NI2P and PI3N substructures regarding the applied bias detect shorter (blue colour) or medium (green colour) and separately longer (red colour) wavelengths of light, respectively. The benefits of the characterisation using first and higher polynomial orders of colour correction are shown and differences discussed. The characterisation was performed by means of 64 Munsell’s and 120 DuPont’s colour chips, which were illuminated with A and D65 standard illuminants [5]. The metameric errors for different combinations of illuminants and colour chips are given and compared. Some benefits of the first order colour
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