Vibration based piezoelectric energy harvesting from unused ambient sources is an efficient approach for a battery-free, sustainable and green power source for self-powered electronics. This paper presents the performance enhancement of a p-n junction based flexible nano-generator (NG). A stable, non-hazardous spiro and zinc oxide (ZnO) p-n junction based NG is proposed. The device performance is compared with a Schottky contact based NG. The experimental study is carried out using the tip excitation method. Most importantly, the contact modification with spiro improves the performance of the device by five times, thereby yielding an open circuit voltage of 300 mV, a short-circuit current density of 220 μA cm-2 and a maximum power density up to 48 μW cm-2 at 0.5 N. Furthermore, performance enhancement is achieved by reducing the external screening and the internal impedance. The results are validated using an RC time constant value derived from the impedance analysis.