Cu-based micro-temperature detectors were fabricated using femtosecond laser reduction of CuO nanoparticles. Cu-based microstructures were directly created by laser scanning on a CuO nanoparticle solution film. Cu-rich and Cu2O-rich microstructures were selectively formed to electrically connect two Cu thin-film electrodes for use in temperature detectors. Cu-rich and Cu2O-rich micro-temperature detectors were fabricated at scanning speeds of 500 and 1000 µm/s, respectively, at a pulse energy of 1.2 nJ. The temperature coefficient of resistance values of the Cu-rich and Cu2O-rich microstructures were positive and negative, respectively; these temperature behaviors are typical of metal and semiconductor materials, respectively.

Micro-temperature sensors, which composed of a Cu2O-rich sensing part and two Cu-rich electrodes, were directly fabricated by femtosecond laser reduction patterning of CuO nanoparticles. Patterning of the microstructures was performed by laser scanning with pitches of 5, 10, and 15 µm. Cu2O-rich micropatterns were formed at the laser scan speed of 1 mm/s, the pitch of 5 µm, and the pulse energy of 0.54 nJ. Cu-rich micropatterns that had high generation selectivity of Cu against Cu2O were fabricated at the laser scan speed of 15 mm/s, the pitch of 5 µm, and the pulse energy of 0.45 nJ. Electrical resistivities of the Cu2O- and Cu-rich micropatterns were approximately 10 Ω m and 9 µΩ m, respectively. The temperature coefficient of the resistance of the micro-temperature sensor fabricated under these laser irradiation conditions was −5.5 × 10−3/°C. This resistance property with a negative value was consistent with that of semiconductor Cu2O.

We fabricated thin-film thermoelectric modules for thermal–photovoltaic hybrid solar generator. Bi0.5Sb1.5Te3 (p-type) and Bi2Te2.7Se0.3 (n-type) thermoelectric thin films were deposited by radio-frequency magnetron sputtering method and patterned to form plane-type thermoelectric modules using lift-off technique. The hybrid module consisted of the thin-film thermoelectric module, a photovoltaic module, a hot mirror, and a near-infrared (NIR) focusing lens. NIR light, which does not contribute to photovoltaic conversion, was separated from solar light using the hot mirror. When the NIR light was focused onto the hot side of the thermoelectric module by the lens, the open voltage generated by the thin-film thermoelectric generator was 78 mV. The total open voltage of the thermal–photovoltaic hybrid generator increased by 1.3% compared to that of the photovoltaic module alone.

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