Impedance spectroscopy and transport mechanism of molybdenum oxide thin films for silicon heterojunction solar cell application

A comprehensive study is reported for temperature-dependent current–voltage (I–V–T), capacitance–voltage (C–V–T), and impedance spectroscopy measurements carried out in the temperature range of 289–413 K for Al/MoO x / n -Si/Al heterojunction solar cell device. Impedance spectroscopy measurements carried out over a broad frequency range (10 2 –10 6 Hz) exhibit semicircle standard Nyquist’s plots implying excellent device stability. An electrical equivalent circuit (EEC) for the device is proposed and the key fitting parameters for the proposed EEC are determined. The C–V–T characteristics of the cell as well as the temperature dependence of the built-in potential, doping gradient, and depletion region width are investigated. Based on the I–V–T measurements, three dominant transport mechanisms are identified in the forward bias regime; thermionic emission (for V < 0.55 V ), trap-space charge limited current due to an exponential distribution of traps (for 0.55 ≤ V < 0.95 V ) and space charge limited current controlled by a single trap state (for 0.95 ≤ V ≤ 2 V ). However, at reverse bias, two different conduction mechanisms, namely Schottky’s emission (SE) and Poole–Frenkel’s (PF) mechanisms are identified. The temperature dependence of the series and shunt resistances, barrier height, ideality factor as well as the photovoltaic performance of the device under illumination are carefully analyzed.