(Georgia Institute of Technology, 2005-01)
Yelundur, Vijay; Nakayashiki, Kenta; Hilali, Mohamed M.; Rohatgi, Ajeet
Solar cell efficiency enhancement resulting from the implementation of a high-sheet-resistance emitter (95 Ω/sq.) in multicrystalline silicon solar cells with screenprinted contacts is demonstrated in this paper. Solar cells on low-cost String Ribbon Si from Evergreen Solar, Baysix
mc-Si from Deutsche Solar, and high-quality float zone silicon with 45 Ω/sq. and 95 Ω/sq. phosphorus-doped n+- emitters are fabricated with RTP-fired screen-printed
contacts and characterized to asses the impact of a highemitter-sheet resistance emitter on cell performance. Screen-printed mc-Si solar cells show an improvement in
Voc of 4-5 mV in most cases that is attributed to the use of the high-sheet-resistance emitter. An appreciable increase
in Jsc by as much as 1.0 mA/cm(2) is also observed due to enhanced blue response identified by internal quantum efficiency measurement.
(Georgia Institute of Technology, 2005-01)
Hilali, Mohamed M.; Nakayashiki, Kenta; Ebong, Abasifreke; Rohatgi, Ajeet
In this study it is found that the efficiency
enhancement (Δη) resulting from the use of a 100 Ω/sq emitter instead of a conventional 45 Ω/sq emitter is substantially enhanced further by surface texturing. This enhancement is greater for textured cells by at least ~0.4% absolute over the enhancement for planar cells, and is mainly due to the greater difference in the front-surface
recombination velocity (FSRV) between the high and low-sheet-resistance emitter textured cells. A FSRV of 60,000 cm/s resulted in a reasonably good V(oc) of ~642
mV for the 100 Ω/sq emitter textured cell. Our investigation of the Ag-Si contact interface shows a more regular distribution of Ag crystallite precipitation for the
textured emitter (mainly at the peaks of the texture pyramids). The high contact-quality resulted in a series resistance of 0.79 Ω-cm, a junction leakage current of 18.5 nA/cm(2) yielding a FF of 0.784. This resulted in a record high-efficiency 4 cm(2) screen-printed cell of 18.8% (confirmed by NREL) on textured 0.6 Ω-cm FZ, with
single-layer antireflection coating.
(Georgia Institute of Technology, 2004-01)
Rohatgi, Ajeet; Kim, Dong Seop; Yelundur, Vijay; Nakayashiki, Kenta; Upadhyaya, A. D.; Hilali, Mohamed M.; Meemongkolkiat, Vichai
This paper presents results on five record-high-efficiency 4 cm(2) solar cells on three different multicrystalline silicon materials through effective hydrogen passivation of bulk defects during cell processing. Silicon ribbon solar cell efficiencies of 18.2% and 17.9% were achieved on EFG and String Ribbon Si cells fabricated with photolithography front contacts, screen-printed Al-doped back surface field, and double layer anti-reflection coating. In addition, high-efficiency, screen-printed, manufacturable cells were achieved on HEM (16.9%), EFG (16.1%), and String Ribbon (15.9%) Si. It is found that proper implementation of a fast co-firing of front and back screen-printed contacts in a belt furnace can significantly enhance the bulk lifetime to ~100 μs and simultaneously produce high quality contacts with fill factors approaching 0.78. The firing process involves fast ramp-up and cooling rates to enhance PECVD SiN(x)-induced hydrogen passivation of defects and the quality of Al back surface field.