Tirunelveli S. Ravi

High efficiency solar cells on direct kerfless 156 mm mono crystalline Si wafers by high throughput epitaxial growth

This paper demonstrates the Direct Gas to Wafer™ technology to produce high quality epitaxial kerfless mono crystalline n-type and p-type silicon wafers. The key aspects of the approach involve anodic etching to form porous Si release layer, growing epitaxial wafers, separation of the epitaxial wafers from the substrate and substrate reuse. The advantages of epitaxial wafers over conventional Cz wafers are discussed. With 156 mm epitaxial wafers, p-type PERC cell has achieved an efficiency of 19.7% and n-type cell has achieved an efficiency above 20%.

Kerfless Epitaxial Mono Crystalline Si Wafers With Built-In Junction and From Reused Substrates for High-Efficiency PERx Cells

This paper proposes a kerfless wafer structure with built-in p-n junctions in n-type silicon wafers grown using Crystal Solars high throughput epitaxy technology. Compared with a conventional p-type emitter by boron diffusion, ion implantation, or epitaxy, the built-in p-type emitter has a reduced and uniform doping concentration and increased thickness. The epitaxially grown wafers and conventional Czochralski (CZ) n-type wafers were processed into solar cells. A best efficiency of 22.5% with epitaxially grown wafers was achieved, with a 6 mV gain in open-circuit voltage, suggesting a high wafer quality and superiority of the deep epitaxial emitter over a standard boron-diffused emitter. Substrate reuse associated with the kerfless epitaxy technology is studied as well, with respect to its impact on solar cell efficiency. The data suggest no degradation in cell efficiency due to substrate reuse.

High-Efficiency Large-Area Screen-Printed Solar Cell on Epitaxial Thin Active Layer With Porous Si Back Reflector Using Standard Industrial Process

Large area 17.3% high-efficiency screen-printed solar cells on a 90-μm-thick epitaxial silicon (epi-Si) active layer with a porous silicon (PSI) back reflector were fabricated using a 182-cm2 epitaxial wafer equivalent (EpiWE) structure and a standard industrial process. The PSI layer was studied and optimized to serve as an efficient back reflector in the finished device. An effective back surface recombination velocity (BSRV) and back internal reflectance (Rb) of 90 cm/s and 88%, respectively, were extracted by PC1D modeling of the EpiWE cell. These values of BSRV and Rb are superior to a standard industrial full Al-BSF Si solar cell, where BSRV and Rb are usually ≥200 cm/s and ~65%, respectively. Model calculations showed very little drop in cell efficiency if the thickness of active epi-Si layer is reduced to ~30 μm because of the good-light trapping provided by the optimized PSI back reflector.