Abstract The temperature and irradiance dependences of the current at maximum power (Imp) and the voltage at maximum power (Vmp) of crystalline silicon photovoltaic (PV) devices are investigated by experiments and numerical simulations based on a single diode model. It is shown that the experimental Imp is nearly constant for temperature variation at fixed irradiances, which agrees with the simulation results being within ±0.02%/K over 273.15–343.15 K (0–70 °C) over the range of parameters represents typical commercial crystalline silicon PV devices. The experimental Imp is nearly proportional to irradiance (G) at fixed temperature, which also agrees with the simulation results that the Imp/G is nearly constant within ±1.3% for the irradiance range between 0.5 and 1.2 kW/m2. Based on these results, a new formula for the temperature correction of Vmp is proposed. It does not require advance information of diode parameters and temperature coefficient. The Imp − Vmp curves which are measured outdoors and corrected to 25 °C by using the formula showed good reproducibility within ±0.13% for many days, which confirms the validity of the formula. The maximum power Pmax can be also precisely estimated by the temperature correction of Vmp. These results are useful for characterizing the performance of crystalline silicon PV devices by using the Imp and Vmp values, which can be measured during their maximum power point tracking (MPPT) operation.