Determination of the Minority Carrier Lifetime in Solar Cells: A Novel Biased OCVD Technique

A new simple method for the determination of the minority carrier lifetime (τ), based on a biased open circuit voltage decay (OCVD) technique, is analyzed. In this case the excitation is given by a pulsed light source (time dependent contribution) added to a continuous background illumination (continuous forward bias). Under appropriate conditions this configuration produces an exponential voltage decay with a time constant which depends on the bias. This constant tends to an effective lifetime for the base region for large values of the bias voltage (typically, 400 to 500 mV). An inexpensive equipment has been developed. Measurements have been made on several crystalline silicon solar cells and on one high-efficiency float-zone silicon solar cell. Experimental results show good agreement with the theoretical model presented and with numerical PC-1D simulations.