2. 5 Characterisation & Simulation Methods for Si Cells
Capacitance, Solar Cell Efficiency, High Efficiency
Summary / Abstract:
High-efficiency solar cells have a high internal capacitance that tends to distort I-V measurements during short voltage sweep times compatible with flash testing. Recently, it was shown that this distortion can be corrected with a weighted average of the measured output currents, using time derivatives of junction voltage as weighting factors. Although this procedure theoretically reproduces the steady-state I-V curve, errors from different sources exist. For example, time derivatives of measurement data are potentially sensitive to even low levels of noise in the original signal. In addition, the correction requires prior determination of the series resistance, which can be susceptible to an error. In this contribution, we investigate errors associated with the capacitance correction. We estimate the magnitude of additional noise that derives from using time derivatives of measurement data as weighting factors, as well as the significance of an error in the series resistance. Further, we provide indications that the physical lower limit for the voltage sweep length is dictated by minority carrier diffusivity. Additionally, we show that the effective minority carrier lifetime of the solar cell can be estimated based on output currents and time derivatives of the junction voltage during forward and reverse sweeps.