We first use a fundamental kinetic model to compare the electron excitation efficiency of different compositions of inert gas mixtures in plasma display panels. Electron excitation efficiency, is an increasing function of the Xe concentration in both the Ne-Xe and He-Xe cases. The fractional increase in efficiency is very small for Xe concentrations higher than ~10%. We also use a two-dimensional self-consistent simulation model to study the effect of the geometric parameters on the operating voltages and the efficiency of a coplanar-electrode plasma display panel cell. For the standard coplanar-electrode geometry it is found that there is a trade-off between high efficiency and low operating voltages as the electrode gap, or other parameters of the upper dielectric are varied, while variation of the sustain electrode width has no significant effect on either the operating voltages or efficiency. Finally, we investigate the performance of several non-standard cell geometry designs involving two-dimensional variations of the coplanar-electrode PDP cell. A PDP cell with modified shape of sustain electrodes is found to have ~20% larger luminous efficiency without substantial increase of the operating voltages. Similar performance improvement is achieved by designs with different shapes of the upper dielectric, or by those involving two different dielectric layers. The dependence of PDP performance on the design parameters of these structures is also investigated.