A photoelectric conversion device taking the form of a thin film and having a substrate exhibiting poor thermal resistance. The device prevents thermal deformation which would normally be caused by local application of excessive heat to the substrate. The device has output terminals permitting the output from the device to be taken out. The output terminals are formed on the surface of the substrate opposite to the photoelectric conversion device. The device further includes electrical connector portions for electrically connecting the electrodes of the device with the output terminals. The present invention also provides a method of treating a substrate having poor thermal resistance with a plasma with a high throughput. The substrate is continuously supplied into a reaction chamber and treated with a plasma. This supply operation is carried out in such a way that the total length of the substrate existing in a plasma processing region formed by electrodes is longer than the length of the electrodes.