Infrared lock-in carrierography (photocarrier radiometric imaging) of Si solar cells

Abstract

Modulated photocarrier radiometric (PCR) imaging (lock-in carrierography) of multicrystalline (mc) Si solar cells is introduced using a near-infrared (NIR) InGaAs camera and a spread superband gap laser beam as an optoelectronic source at low modulation frequencies $\left(<10\text{Hz}\right)$ or point-by-point scanning PCR imaging with a focused laser beam at high (kilohertz) frequencies. PCR images are supplemented by quantitative PCR frequency scans and compared to NIR optical reflectance, modulated electroluminescence (MEL) and modulated photovoltage (MPV) images. Noncontact PCR imaging is controlled by the photoexcited carrier diffusion wave and exhibits very similar images to contacting MEL and MPV. Among these methods it exhibits the highest contrast and sensitivity to mechanical and crystalline defects in the substrate at lock-in image frequencies in the range of the inverse recombination lifetime in the quasineutral region (bulk).