Recent advances in wireless electronics have outpaced concurrent advances in battery technology, and this has led to the emergence of vibrational energy harvesting as an alternative source of energy for low-power wireless devices. In particular, piezoelectric materials have been widely studied as an energy conversion mechanism due to their ability to generate electric potential in response to applied mechanical strain. This paper investigates the response of a buckled piezoelectric beam to harmonic base excitation. Forced buckled structures may exhibit snap-through behaviour, in which the structure rapidly deforms from one stable configuration to another. Of particular interest to this study is the effect of an attached mass on persistent snap-through behaviour, which has clear applications to energy harvesting due to its relatively large amplitude motion. It is shown experimentally that the addition of a small mass to the centre of the beam significantly broadens the frequency range over which snap-through is observed, which leads to increased power output over those frequencies. Additionally, it is shown that adding a centre mass can lower the threshold forcing amplitude above which persistent snap-through can occur. Finally, it is shown that for a particular forcing condition, there exists a nearly linear relationship between the applied mass and the power output by the snap-through response. A theoretical model was developed to describe the system's behaviour, which agreed with experimental findings that an attached mass leads to broadened frequency response and a lower threshold for large amplitude response.