(Georgia Institute of Technology, 2003-05)
Kim, Dong Seop; Gabor, A. M.; Yelundur, Vijay; Upadhyaya, A. D.; Meemongkolkiat, Vichai; Rohatgi, Ajeet
We have fabricated 4 cm(2) cells on String Ribbon Si wafers with efficiencies of 17.8% using a combination of laboratory and industrial processes. These are the most
efficient String Ribbon devices made to date,
demonstrating the high quality of the processed silicon and the future potential for industrial String Ribbon cells. Cofiring
PECVD (Plasma Enhanced Chemical Vapor
Deposition) silicon nitride (SiN(x)) and Al was used to boost the minority carrier lifetime of bulk Si. Photolithography front contacts were used to achieve low shading losses and low contact resistance with a good blue response. The firing temperature and time were studied with respect to the trade-off between hydrogen retention
and aluminum back surface field (Al-BSF) formation. Bulk defect hydrogenation and deep Al-BSF formation took place in a very short time (~1 sec) at temperatures
higher than 740 degrees C.
(Georgia Institute of Technology, 2003-05)
Rohatgi, Ajeet; Yelundur, Vijay; Jeong, Ji-Weon; Kim, Dong Seop; Gabor, A. M.
This paper summarizes our progress in fabricating record-high efficiency ribbon Si solar cells with screen-printed
and photolithography defined contacts. We have developed and optimized rapid thermal processing enhanced SiN(x)-induced hydrogenation to achieve record-high
efficiency screen-printed EFG (15.9%) and String Ribbon (15.6%) cells and a high-efficiency String Ribbon
cell (17.8%) with photolithography defined contacts. A low-frequency SiN(x) film and a two-step RTP firing process were critical in achieving high-efficiency screenprinted
cells. Step 1 provides SiN(x) induced hydrogenation and forms an aluminum doped back surface field. Step 2 is designed for Ag grid firing and includes rapid cooling to
retain hydrogen introduced in Step 1.