ION IMPLANTATION AND ANNEALING FOR THIN-FILM CRYSTALLINE SOLAR CELLS
A back contact back junction thin-film solar cell is formed on a thin-film semiconductor solar cell. Preferably the thin film semiconductor material comprises crystalline silicon. Base regions, emitter regions, and front surface field regions are formed through ion implantation and annealing processes.
1 . A method for making base regions in a thin-film crystalline silicon substrate, the method comprising:
forming openings in a dielectric layer for base contacts on a thin-film crystalline silicon substrate, wherein said openings form a patterned dielectric layer;
implanting ions of an dopant element in said thin-film crystalline silicon substrate within said patterned dielectric layer to selectively introduce said dopant element at said base contacts, said patterned dielectric used as an ion implantation mask;
activating said implanted dopant element to form electrically active doped base contacts;
forming emitter contacts on said thin-film crystalline silicon substrate; and
forming metallization contacts on said emitter contacts and said base contacts.
2 . The method of claim 1 wherein said dopant element comprises at least one element from the group of phosphorus, arsenic, antimony, and indium in conjunction with an n-doped epitaxial silicon substrate.
3 . The method of claim 1 , further comprising the step of forming a crystalline thin-film silicon substrate, the steps comprising:
forming a porous sacrificial layer on and substantially conformal to the surface of a silicon template;
subsequently depositing an epitaxial silicon layer on said sacrificial layer;
performing a plurality of solar cell processing steps including said ion implantation process; and
releasing said epitaxial silicon layer from said silicon template through a mechanical release or epitaxial lift off process.
4 . The method of claim 1 , wherein said silicon substrate is an n-type silicon substrate and the base contact doping element is phosphorous (P), arsenic (As), or antimony (Sb).
5 . The method of claim 1 , wherein said silicon substrate is a p-type silicon substrate and the base contact doping element is boron, gallium, or aluminum.
6 . The method of claim 1 , wherein said opening for base contacts is performed using laser ablation.
7 . The method of claim 6 , wherein said laser ablation is pulsed pico-second laser ablation.
8 . The method of claim 6 , wherein said laser ablation is pulsed femto-second laser ablation.
9 . The method of claim 1 , wherein said activating said implanted dopant element is performed using furnace annealing.
10 . The method of claim 1 , wherein said activating said implanted dopant element is performed using laser annealing.
11 . The method of claim 10 , wherein said laser annealing is pulsed nanosecond laser annealing.
12 . The method of claim 1 , wherein the base and emitter contacts are patterned in parallel linear regions.
13 . The method of claim 1 , where the base and emitter contacts are formed as discrete islands.
14 . The method of claim 1 , wherein the percent of base opening can be in the range from about 0.5% to 10%.
15 . The method of claim 1 , where laser ablation is carried out using laser with wavelength being IR, green, or UV, or any wavelength between.
16 . The method of claim 1 , where the surface concentration of dopants in the base may be from 1×10 19 to 1×10 21 /cm3, implanted at a depth of 0.1 to 5 μm.
17 . A method for making a front surface field region in a thin-film crystalline silicon substrate, the method comprising:
implanting dopant atoms on the front side of a thin-film crystalline silicon substrate, wherein the dopant element has a peak concentration in the range of 1E16 to 1E20 cm −3 ; and
activating said implanted ions using laser annealing using a continuous wave (CW) laser or a pulsed laser to form a front surface field on said thin-film crystalline silicon substrate.
18 . The method of claim 17 , wherein said dopant element comprises at least one element selected from the group of phosphorus, arsenic, antimony, and indium in conjunction with an n-doped epitaxial silicon substrate.
19 . The method of claim 17 , wherein said front surface field has a depth in the range of 10 angstroms to about 1 micron on the front side of said thin-film crystalline silicon substrate.
20 . The method of claim 17 , wherein said thin-film crystalline silicon substrate is passivated with a passivation layer deposited at a temperature less than 250° C.
21 . The method of claim 17 , wherein said dopant element comprises at least one element selected from the group of phosphorus, arsenic, antimony, and indium in conjunction with an n-doped silicon substrate.
22 . The method of claim 17 , wherein the peak concentration of the dopant element is at the interface of the silicon film and the said passivation layer.
23 . The method of claim 17 , wherein the incident angle of the laser beam is controlled based on a dielectric stack on the front surface of said substrate to prevent from heating the back plane as it undergoes full internal reflection.
24 . The method of claim 17 , wherein said laser has a wavelength less than or equal to 1064 nanometers.
25 . The method of claim 24 , wherein said passivation layer is chosen from the group consisting of SiN, amorphous silicon/SiN stack, oxide/SiN stack, or silicon oxynitride with and without an oxide underlayer, and silicon carbide.
26 . The method of claim 24 , wherein the passivation layer is deposited after the ion implantation and laser anneal.
27 . The method of claim 24 , wherein the ion implantation and anneal is carried out after the passivation layer is deposited.
28 . A method for making selective emitter regions in a thin-film crystalline substrate, the method comprising:
forming first openings in a parallel linear region pattern for emitter contacts on a thin-film crystalline silicon substrate;
selectively implanting ions of an dopant element in said thin-film crystalline silicon substrate at said emitter contacts;
activating said implanted ions to form doped emitter contacts; and
forming metallization contacts on said emitter contacts and base contacts on said thin-film crystalline silicon substrate.
29 . The method of claim 28 , wherein said silicon substrate is an n-type silicon substrate and said emitter contact doping element is boron, gallium, or aluminum.
30 . The method of claim 28 , wherein said silicon substrate is a p-type silicon substrate and said emitter contact doping element is phosphorous (P), arsenic (As), indium (In), or antimony (Sb).
31 . The method of claim 28 , wherein said silicon substrate is a p-type silicon substrate and a base contact doping element is boron, gallium, or aluminum.
32 . The method of claim 28 , wherein the opening for emitter is performed using pulsed laser ablation.
33 . The method of claim 28 , wherein the implant activation is performed using furnace annealing.
34 . The method of claim 28 , wherein the implant activation is performed using laser annealing.
35 . The method of claim 28 , wherein said base and emitter contacts are discrete islands.