Flexible UV photodetectors have immense potential for next-generation wearable UV sensors, dosimeters, etc. Moreover, flexible substrates can make use of piezoelectric properties of ZnO to function as nanogenerator. We have developed ZnO nanowalls network-based visible-blind UV photodetector, over Al foil by simple and low-cost hydrothermal technique. Choosing Al foil as a substrate has provided three-fold advantages viz. Al doping, nanowalls network growth, and flexibility. The proposed ultralow voltage UV photodetector demands very low power and therefore could potentially lengthen the battery discharge time. The device has demonstrated a high responsivity and detectivity of 0.26 A/W and 4.5 x 10-10 cm.Hz1/2.W -1 respectively, at just 0.1 V applied bias. Additionally, a prominent UV sensitive piezoelectric response, having dark voltage to photovoltage ratio of 24.5 has been demonstrated that has made the device a potential candidate for fast response time, self-powered photodetector.