Estimating the effect of LED spectra on EQE measurement in solar cells

Light emitting diodes (LED) are increasingly being used as light sources in studying solar cells due to their high power and bulb lifetimes. While LEDs provide higher power, they have a comparatively broad emission spectrum. This study compares the effect of using an LED based illumination on measurements of the external quantum efficiency (EQE) for silicon solar cell with monochromatic light source. An analytical approach is shown to quantify the impact of using an LED by approximating the LED spectral emission as the sum of multiple Gaussian curves. Furthermore a method that corrects the impact of the finite spectral width of LEDs on the measured EQE is presented. It is shown that after applying the correction method to the measured EQE, the error developed can be reduced from 3-5% to under 0.5% absolute error. This correction method was tested on a home built LED based EQE tool.