Uniform thermal processing by internal impedance heating of elongated substrates
An elongated substrate may be heated in a roll processing system. At least a portion of the elongated substrate is loaded into the roll processing system. A sufficient electrical current is caused to flow in the portion of the elongated substrate to heat the portion to a desired temperature. The heating may be either resistive or inductive. The roll processing system may be a roll-to-roll type where the substrate moves as a portion of it is heated. Alternatively, the substrate may be wound into a coiled substrate and the turns of the coil insulated against undesired electrical contact. The entire coiled substrate may then be heated either resistively or inductively.
1. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system; and
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature, wherein causing includes:
electrically contacting first and second leads to the portion of the elongated substrate at spaced apart locations;
applying an electrical voltage between the first and second leads whereby an electric current flows through the substrate between the first and second leads.
2. The method of claim 1 wherein the substrate moves past the first and second leads while the electrical voltage is applied between the first and second leads.
3. The method of claim 1 wherein the first lead electrically contacts the elongated substrate proximate a first edge and the second lead electrically contacts the elongated substrate proximate a second edge whereby the electric current flows across a width of the elongated substrate.
4. The method of claim 1 wherein the first and second leads are configured such that the electric current flows along a length of the elongated substrate.
5. The method of claim 1 wherein causing a sufficient electrical current to flow in the portion of the elongated substrate includes:
disposing an inductor proximate the portion of the elongated substrate; and
applying high-frequency power to the inductor.
6. The method of claim 5 wherein the inductor is disposed above the portion of the elongated substrate.
7. The method of claim 5 wherein the inductor is disposed below the portion of the elongated substrate.
8. The method of claim 5 wherein the substrate moves past the inductor while the high-frequency power is applied between the inductor.
9. The method of claim 5 further comprising controlling power from the source of high-frequency power using one or more temperature or flux sensors coupled to a source of the high-frequency power in a closed control loop.
10. The method of claim 1 further comprising loading at least a portion of the elongated substrate into the roll processing system includes coiling the elongated substrate into a coiled substrate.
11. The method of claim 10 , further comprising insulating adjacent turns of the coiled substrate against undesired electrical contact.
12. The method of claim 10 wherein causing a sufficient electrical current to flow in the portion of the elongated substrate includes:
electrically contacting a first lead at or near a first edge of the coiled substrate and electrically contacting a second lead at or near a second edge of the of the coiled substrate; and
applying an electrical voltage between the first and second leads, whereby the electrical current flows across a width of the coiled substrate.
13. A method for heating an elongated substrate in a roll processing system, comprising:
loading at least a portion of the elongated substrate into the roll processing system;
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature; and
forming a nascent photovoltaic absorber layer containing one or more elements of group IB and one or more elements of group IIIA on an aluminum foil substrate.
14. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system;
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature, wherein causing comprises:
electrically contacting first and second leads to the portion of the elongated substrate at spaced apart locations;
applying an electrical voltage between the first and second leads whereby an electric current flows through the substrate between the first and second leads; and
focusing or defocusing the electric current with a magnetic field.
15. The method of claim 14 , further comprising controlling the magnetic field using one or more temperature sensors, magnetic field sensors or current flux sensors coupled to a magnet controller in a closed control loop.
16. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system;
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature, wherein causing comprises:
electrically contacting first and second leads to the portion of the elongated substrate at spaced apart locations;
applying an electrical voltage between the first and second leads whereby an electric current flows through the substrate between the first and second leads; and
controlling the electrical voltage using one or more temperature sensors, magnetic field sensors or current flux sensors coupled to a power supply in a closed control loop.
17. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system; causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature, wherein causing comprises:
disposing an inductor proximate the portion of the elongated substrate; and
applying high-frequency power to the inductor
focusing or defocusing the electric current with a magnetic field.
18. The method of claim 17 , further comprising controlling the magnetic field using one or more temperature sensors, magnetic field sensors or current flux sensors coupled to a magnet controller in a closed control loop.
19. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system;
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature;
wherein loading at least a portion of the elongated substrate into the roll processing system includes:
coiling the elongated substrate into a coiled substrate; and
insulating adjacent turns of the coiled substrate against undesired electrical contact;
wherein causing a sufficient electrical current to flow in the portion of the elongated substrate includes:
electrically contacting a first lead at or near a first end of the coiled substrate and electrically contacting a second lead at or near a second end of the of the coiled substrate; and
applying an electrical voltage between the first and second leads, whereby the electrical current flows along a length of the coiled substrate.
20. The method of claim 19 further comprising measuring a temperature of the coiled substrate with a sensor and controlling a source of the high-frequency power with a signal from the sensor using a closed-loop circuit.
21. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system;
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature;
loading at least a portion of the elongated substrate into the roll processing system includes coiling the elongated substrate into a coiled substrate; and
insulating adjacent turns of the coiled substrate against undesired electrical contact;
wherein causing a sufficient electrical current to flow in the portion of the elongated substrate includes:
electrically contacting a first end of the coiled substrate to a second end of the coiled substrate;
placing the coiled substrate within an induction coil; and
energizing the induction coil to inductively heat the coiled substrate.
22. A method for heating an elongated substrate in a roll processing system, comprising the steps of:
loading at least a portion of the elongated substrate into the roll processing system;
causing a sufficient electrical current to flow in the portion of the elongated substrate to heat the portion to a desired temperature;
forming a nascent absorber layer containing one or more elements of group IB and one or more elements of group IIIA on an aluminum foil substrate;
rapidly heating the nascent absorber layer and/or substrate from an ambient temperature to a plateau temperature range of between about 200° C. and about 600° C.;
maintaining the absorber layer and/or substrate in the plateau temperature range for between about 2 minutes and about 30 minutes; and
reducing the temperature of the absorber layer and/or substrate.
23. The method of claim 22 wherein rapidly heating the nascent absorber layer and/or substrate includes increasing the temperature of the absorber layer and/or substrate at a rate of between about 5° C./sec and about 150° C./sec.