Temperature uniformity in a photovoltaic (PV) module is critical to accurately measure module performance parameters and temperature coefficients. In the case of indoor flash solar simulators, a uniform temperature among all the cells within a test module is maintained using a specialized thermal setup or an air conditioned environment. However, maintaining uniform module temperature in all the cells of a module under prevailing uncontrolled outdoor field conditions on clear sunny days has been a challenge. This study quantitatively determines the extent of temperature non-uniformity, and the influence of 'spatial' temperature distribution on the accuracy of module performance parameters and temperature coefficients. An experimental approach to improve temperature uniformity under prevailing field conditions is also presented to obtain outdoor performance data and to possibly improve field performance with less influence of temperature variability. Results indicate that better temperature uniformity and more accurate performance data can be obtained by thermally insulating the inner and outer surfaces of the module frame.