Temperature dependence of the optical gap of diamond-like carbon films investigated by a piezoelectric photothermal spectroscopy

Temperature dependences of the optical gap of diamond-like carbon (DLC) films were investigated by using a piezoelectric photothermal (PPT) spectroscopy, that detects the nonradiative transition of photoexcited electrons. Since the PPT signal intensity is expected to be proportional to its optical absorption coefficient, the optical gap was estimated by a Tauc plot. The temperature coefficient of the optical gap energy was found to be very small compared with that of other semiconductor such as Si. This result implies that the device performance is expected to be stable by temperature change and the DLC films are excellent as the next generation solar cells materials.