The equivalent single-side illumination method was proposed as the possible way to measure the bifacial photovoltaic devices. To verify the equivalent single-side illumination method, we compared the current–voltage ( I–V ) characteristic measurement of bifacial single-cell laminates under double-side and equivalent single-side illumination conditions. The results showed that the short-circuit current ( $I_{{\text{sc}}}$ ) and the open-circuit voltage ( $V_{{\text{oc}}}$ ) of each method were almost consistent, whereas the maximum power ( $P_{{{\max}}}$ ) of the double-side illumination method was higher than that of the single-side method under a range of different combinations of front and rear irradiation. To analyze the reason for this difference, we applied the penalty-based differential evolution method to further extract the one-diode model parameters of bifacial single-cell laminates. Among all the parameters, it was found that the series resistance ( $R_{s}$ ) measured with both methods was obviously different. As a result, an $R_{s}$ -correction model was accordingly proposed to correct the $P_{{{\max}}}$ measured with the equivalent single-side illumination method.