Potential for improvement on DC\DC converters tailored for photovoltaics by ZnO-based TFT

The output power of photovoltaics depends on weather conditions, like illumination and temperature, and the operation point which was relied on the load or controlled by different functions of converters. DC\DC converters, such as boost, bulk, and booster-bulk converters, are commonly used in the maximum power point tracking (MPPT) of photovoltaics. The components of DC\DC converters mainly include the inductance, MOSFET, and the capacity, and the working principle of that is modulating electrical energy in the converter by the on/off switching, i.e. the duty cycle of pulse width modulation (PWM), of metal-oxide-semiconductor field effect transistor (MOSFET) to vary the operation point of photovoltaics. To maintain the low ripple on DC current limited by the short size of the inductance component due to the consideration of magnetic field emission, DC\DC converters operated in the condition of the high switching frequency are needed. Unavoidably, it results in more switching loss in the inductance and MOSFET components. Instead of the amorphous silicon usually used to fabricate the oxide layer of MOSFET, we employed ZnO thin film as the oxide layer between Al source/drain electrode pads and SiO2/p-Si substrates to fabricate ZnO-based thin film transistors (TFT). From experimental results, ZnO-based TFT has only the similar or higher mobility and on/off ratio but also similar or lower resistance than amorphous silicon TFT. Therefore those advantages of ZnO-based TFT are potential to improve the performance of DC\DC converters operated in high frequency. In addition, ZnO thin film is the transparent oxide thin film because of its large band gap of 3.3eV. ZnO-based TFT fabricated on indium-tin-oxide (ITO) glass substrates are suitable to integrate with photovoltaics for the printed circuit. Besides, the dark saturation drain current of ZnO-based TFT is about an order of magnitude smaller than the drain current of that under UV illumination. It indicates that the photoelectric effect in ZnO layer is possible to develop photovoltaic devices.