TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Apparatus: The in-line production apparatus includes a device for detecting the deposited amount of constituents of the CIGS film. The detecting device is X-ray fluorescence (XRF) device (20), an energy dispersion X-ray spectroscopy (EDX) device, or a profilometer. Additional sensor(s) is connected to an input of respective controllers to measure the physical parameter upstream and/or downstream the reference transition point. The controller is adapted to change the relative amount of copper versus indium and gallium. An X-ray fluorescence composition measurement device measures the total deposited amounts of each element (copper, gallium, indium, selenide), and the thickness and composition of the deposited CIGS layer.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: Detection is performed at location(s) as seen in a direction over the width of a substrate. A substrate provided with molybdenum back contact layer moves through the CIGS process chamber. The physical parameter is monitored at two points, one at each side of the position of CIGS layer in the process chamber at the reference transition point to detect the position where the transformation occurs, with the position referred to as reference position. Heating elements are arranged at each side of the position at which the transition occurs, and the method includes holding the power delivered to the substrate constant and measuring a temperature difference at two adjoining heating elements at the reference position, or holding the temperature of substrate and deposited CIGS film constant by supplying individually controlled power to the heating elements and measuring a difference in the power delivered at two adjoining heating elements at the reference position. Pairs of sensors distributed over the width of process chamber are used for detection at the two points, and each sensor pair is assigned with a respective set of evaporation sources (11-13). The evaporation flows in each set of evaporation sources are adjusted to bring the respective transition points back to their reference transition positions. Alternatively, a pair of sensors is used for detection at the two points, and copper flux is adjusted in each set. The method may include detecting the deposited amount of constituents of the CIGS film, and providing sets of evaporation sources in rows over the width of a substrate and controlling the evaporant fluxes in the respective rows. Alternatively, composition control of CIGS solar cells includes measuring the individual amounts of elements in the deposited layer by providing sets of evaporation sources in rows over the width of a substrate, measuring the individual amounts of elements in the deposited layer in each row, and controlling the evaporant fluxes in the respective rows to provide a CIGS film of uniform composition of elements.Preferred Parameters: The physical parameter is related to the emissivity of the CIGS layer. It may be heat capacitivity or resistivity. The physical parameter relates to intensity of light reflected by or transmitted through the deposited CIGS film or to intensity of specular light in relation to intensity of reflected light.