Evaluating BP Solar's Mono<sup>2 ™</sup> material: Lifetime and cell electrical data

Abstract

Single crystal Silicon has been produced using a cast-in-place process usually used for multicrystalline ingot production. This Mono <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 TM</sup> material produces higher cell efficiencies compared to multi crystalline silicon material with the same average minority carrier lifetime. Profiles of lifetime through the height of the brick and across the ingot demonstrate rough equivalency in bulk lifetime between Mono <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 TM</sup> and multi material. However, the standard deviation of lifetime in wafers is smaller for the Mono <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 TM</sup> material. This quality difference accounts for about half of the potential efficiency gain in Mono <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 TM</sup> material, while the rest of the gain, primarily in J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> , is derived from the ability to form pyramidal light trapping texture on the (100) surface. Minority carrier lifetime data is compared with cell electrical data from the same collection of ingot positions. Open circuit voltage and short circuit current correlate well to some degree with bulk lifetime, while fill factor is independent both of bulk lifetime and position in the ingot.