Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS), has been employed in a wide range of applications owing to its good film-forming properties, high transparency, tunable conductivity, and good thermal and environmental stability. In piezoelectric nanogenerators (PENGs), p-type PEDOT:PSS has been used to form a p-n junction with n-type ZnO nanorods, which slows down the screening of the piezoelectric polarisation to increase the generated output voltage. Optimizing the conductive property of PEDOT:PSS is therefore a potential way to improve the performance of a PENG by controlling the screening effect and internal resistance of the device. In this work, ethylene glycol (EG) is added to the PEDOT:PSS layer in a ZnO PENG to modify its conductivity. Doping with EG, induces a change in conformation of the PEDOT which transform from a coil shape to expanded-coil or linear shapes as confirmed by Raman spectroscopy. The conductivity of the PEDOT:PSS layer is enhanced and the internal resistance of the PENG device is reduced, producing a higher current output. However, at the same time, devices using higher EG doping levels produce reduced voltage output, which is related to the rapid screening of the developed polarisation. Specifically, the optimal EG content was identified at 2.5%; although this resulted in a slight 4.0% reduction in voltage output compared to undoped devices, the current output increased by 41.6%, ultimately leading to a 33.1% improvement in peak power output. Therefore, we find that a balance between reducing the device resistance, which increases current output, and supressing the screening effect, which increases voltage output, is required to produce an optimum power output from the devices.