Characterizing Device Efficiency Potential from Industrial Multi-Crystalline Cell Structures Composed of Solar Grade Silicon

This comparative study is presented to illustrate several key relationships between impurity density in the silicon wafer and device performance within a baseline silicon nitride firing-through cell process. Results are given as a function of solidification fraction on multi-crystalline production ingots, and link cell investigations to the solar grade silicon (SoG-Si) blends. Illuminated current-voltage characteristics of SoG-Si cells having a compensated, net acceptor concentration up to 3 x 10 cm show equivalent conversion efficiencies relative to control cells (η > 15.3%), and excellent open circuit voltage measurements (Voc > 625 mV). As net acceptor concentration is further increased, recombination influences minority carrier lifetime and offsets corresponding increases in open circuit voltage. To identify metallic impurity species responsible for recombination, laser beam induced current and microwave detected photo-conductance decay mappings are combined with elemental analysis from secondary ion mass spectrometry in the phosphorus-gettered region. Upon optimizing diffusion conditions to create a tailored emitter profile, enhanced short circuit current values were obtained (Jsc > 32.5 mA cm). Infrared luminescence images of reverse biases cells are paired with leakage currents measured during dark current-voltage characterization and expressed as a function of net-ionized dopants. Light induced degradation findings on SoG-Si cells are contrasted with other work and proposed explanations from elemental analysis offered. Near-term performance extensions through advanced cell constructions are explored on full size (η > 16.1%) and on small area devices (η > 17.8%) to illustrate SoG-Si feedstock potential.