Performance and Reliability In Compensated Elkem Solar Silicon

REC Solar Norway's solar cell silicon (ESS), produced via a metallurgical production route with a considerably lower energy consumption than the competitors production of polysilicon, is used for making high efficient solar cells of different types (Al-BSF og PERC-celler) in this project - aiming for a comparison to regular reference cells based on polysilicon. Especially the performance during realistic operating temperatures has been a focus to be able to explain better the improved production from solar panels based on ESS shown in earlier RCN-funded projects. During the project period earlier hypothesis linked to improved temperature coefficients of compensated material like ESS have been confirmed. In addition the general understanding of the connections between parameters influencing the performance of solar cells at elevated temperatures has increased, which has resulted in the development of modeling tools able to predict the performance within an accuracy of approximately +/- 10%. The work has resulted in several publications, which have also been presented in international conferences.

Bidrag til fokus og økt forståelse for solcellers virkemåte - spesielt som funksjon av temperature - ved forskningsmiljøer I Norge. Forståelsesmodell for ytelse til solceller som funksjon av temperature, som også inkluderer og synliggjør fordeler ved kompensert silisium (som ESS). Vitenskapelig grunnlag bak "selling point" for REC sine solcellepaneler basert på ESS. Publisering av resultater ved internasjonale konferanser og I international tidsskrifter. Synliggjøring av fordelaktige effekter knyttet til ytelse til solceller ved høye temperature gjennom modultester hos internasjonal uavhengig tredjepart.

The proposed project aims to improve the market position of Elkem Solar Silicon® (ESS®) in the rapidly growing, global market for crystalline silicon (Si) solar cells. ESS® is produced using a proprietary metallurgical purification route which uses significantly less energy than most competing Si production routes. Because of this, the resulting Si material contains more of the dopants phosphorus and boron, and the resulting material is therefore compensated. Nevertheless, cells made from ESS® have been shown to exhibit comparable power production compared to conventional Si material. High performance multicrystalline Si (HPMC-Si) is rapidly replacing conventional mc-Si in solar cell production, and is also introduced into high efficiency cell architectures. The main goal of this project is to demonstrate that ESS® may be used in the production of both HPMC-Si Si wafers and advanced solar cells with efficiency exceeding 20%. In order to reach this goal it will be necessary to: a) Determine the mechanisms behind the beneficial temperature coefficients in ESS® material, and investigate whether the improved performance relative to reference material at elevated temperatures is observed also in HPMC-Si material. b) Obtain a quantitative description of light-induced degradation in HPMC-Si wafers made from ESS® and establish suitable processes for reducing or permanently reversing this effect. The project draws substantial benefits from a stronger integration of Elkem Solar and REC Solar, and measurements will therefore be performed on a very large number of wafers and cells made from different types of Si feedstock. In addition, a deeper fundamental understanding of solar cells made from compensated silicon will be obtained by developing and using numerical device simulation tools. The combination of carefully designed experiments, a large set of experimental data and theoretical modelling will provide a solid framework for further improvements of the ESS® material.