TECHNOLOGY FOCUS - ELECTRONICS - Preferred Components: The light source is a laser. The light source is a high power LED array. The light source has a wavelength of 400-550 nm.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Apparatus: The apparatus further comprises: cooling device positioned to cool the web during or after illumination. The apparatus further comprises printing station for printing the thermocleavable polymer layer on to the web. Preferred Components: The cooling device is a cooling roller located opposite the illumination source. The source of illumination is a light emitting diode (LED) array. The printing station comprises a printer, and device for surface treatment of the surface of the web to be printed. The printing station further comprises device for drying the printed thermocleavable layer.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The illumination is carried out in a series of pulses. The pulse duration is in the millisecond range. The light source provides a field of illumination which is moved relative to the thermocleavable polymer layer. The thermocleavable polymer layer is illuminated from both faces. The heat sensitive component is cooled during illumination. A mask is interposed between the light source and the thermocleavable polymer layer in order that selected areas of the thermocleavable polymer layer are illuminated. The method further involves washing the thermocleavable polymer layer after illumination to remove uncleaved areas of the layer. Preferred Components: The thermocleavable layer has an absorbance of around 1, and where the heat sensitive component has an absorbance of less than 0.1. The heat sensitive component is present in an amount of at least 75% by weight or by volume of the combined weight or volume of the heat sensitive component and the thermocleavable layer. The heat sensitive component is a polymer film on which the thermocleavable polymer layer is provided. The heat sensitive component is transparent to the light wavelength range used to illuminate the thermocleavable polymer layer. The thermocleavable polymer layer and the heat sensitive component are comprised in a photovoltaic device. The thermocleavable polymer is a hole-conducting polymer. The thermocleavable polymer is a polythiophene (PT) or poly(phenylenevinylene) (PPV) derivative. The polymer has thermocleavable side chains which are ester groups that can be cleaved to give the free carboxylic acid group. The polymer is poly (3-(2-methylhex-2-yl)oxycarbonyldithiophene) (P3MHOCT), poly-((3'-(2,5,9-trimethyldecan-2-yl)-oxy-carbonyl)-(2,2';5',2'')terthiophene-1,5''-diyl)-co-(2,3-diphenylthieno(3,4-b)pyrazine-5,7-diyl)) (P3TMDCTTP) or poly-((3'-(2,5,9-trimethyldecan-2-yl)-oxy-carbonyl)-(2,2';5',2'') terthiophene-1,5''-diyl)-co-(benzo(c)(1,2,5)thiadiazole-4,7-diyl)) (P3TMDCTBT). EXAMPLE - An approximately 100 nm thick poly(3-(2-methylhex-2-yl)oxycarbonyldithiophene) (P3MHOCT) film was spincoated onto a substrate containing 0.25 mm thick polyethyleneterephthalate (PET) film with a 75 nm thick layer of indium-titanium-oxide (ITO) on it. The film absorbance was around 1 for a 100 nm thick film of pure P3MHOCT. The P3MHOCT film on the substrate was mounted in a holder for illumination. Illumination was carried out using a diode pumped Nd-YAG laser of 532 nm wavelength and having a maximum output power of 4.9 W. One 25 ms pulse with a spot size of 0.625 mm (resulting in an energy delivery to the layer of approximately 40 J cm-2) was delivered manually using an acousto-optic modulator to convert P3MHOCT through the entire 100 nm film to poly (3-carboxydithiophene) (P3CT). Conversion of the P3MHOCT to P3CT was determined by rubbing the polymer film with a cotton bud soaked in chlorobenzene. The fully converted film remained insoluble in the solvent, whereas the unconverted or partially converted film was soluble in the solvent and was seen as a red coloring on the cotton bud. The conversion was also confirmed by observing the IR spectrum of the film using attenuated total reflection-IR (ATR-IR). Illumination under the same conditions but using a single pulse with a duration of 100 ms giving approximately 160 J cm-2 resulted in conversion to polythiophene (PT). Conversion to PT was determined by observing the IR spectrum of the film where the IR spectrum of PT did not contain a C=O stretch at ca 1700 cm-1, whereas this peak was present in the spectrum of P3CT.