Due to the structure of photovoltaic/thermal (PV/T) collectors, non-uniform distribution of solar irradiance and PV cell temperature is inevitable. In traditional models, uniform or 1D distribution of irradiance and temperature were adopted widely to analyze the output performance, which cannot obtain an accurate description on the dynamic behavior of the PV/T system. Thus, a novel 2D irradiance-temperature coupling model for the performance characterization of flat-plate PV/T system was proposed in this study. Results suggest that the non-uniform distribution of irradiance exerted a dramatic effect on photovoltaic efficiency but a modest influence on photothermic efficiency. As the ratio of frame shadow on PV cells changed from 0% to 80%, the photovoltaic efficiency decreased by 42.26% and the photothermic efficiency increased by 9.81%. By contrast, the flow rate had a stronger effect on the photothermic efficiency than the photovoltaic efficiency. As the flow rate increased from 0.005 kg/s to 0.03 kg/s (velocity changing from 0.0112 m/s to 0.0674 m/s in the copper tube), the photovoltaic efficiency increased from 9.46% to 9.54% and the photothermic efficiency improved from 32.62% to 35.83%. Moreover, a parallel electrical circuit layout has a greater total output with a value of 2594.99 MJ/m(2). (C) 2020 Elsevier Ltd. All rights reserved.