Gencoa Limited, Physics Road, Liverpool, UK 2. Gencoa USA, Davis, CA, USA 3. Nano4Energy, Madrid, Spain 4. Universidad Autonoma de Madrid, Spain

Transcription

1 Luxel.com A NOVEL SENSOR FOR Selenium VAPOUR DEPOSITION MONITORING AND CONTROL V. Bellido-Gonzalez 1, D. Monaghan 1, J. Brindley 1, B. Daniel 1, R. Brown 1, F. Papa 2, A. Wennberg 3, I. Fernández 3, M.Leon 4 1 Gencoa Limited, Physics Road, Liverpool, UK 2 Gencoa USA, Davis, CA, USA 3 Nano4Energy, Madrid, Spain 4 Universidad Autonoma de Madrid, Spain

2 Structure of the talk Introduction to Se use for CIGS solar cells & the need for optimization Current methods for measurement overview The new sensor and measurement examples Closed loop control of Se and S delivery Conclusions 2

3 CIGS thin film solar cells are manufactured in a 2 step or 1 step process Elemental Se is required in both cases Encyclopedia of Sustainability Science and Technology pp Solar Cells, Chalcopyrite-Based Thin Film Hans-Werner Schock

4 But it is accepted that the existing technologies cannot approach the theoretical maximum efficiencies of 30% In order to achieve the higher efficiencies total flexibility to readily change layer compositions and layer combinations with a reliable process is required. A pure sputter based approach can achieve this so long as the current challenges of the Se and S delivery are overcome. The biggest technical challenge is lack of good control of the Se and S gas combined with lack of a fast feedback and precise dosing method.

5 But it is accepted that the existing technologies cannot approach the theoretical maximum efficiencies of 30%

6 Different methods are available to measure Se vapour in a vacuum Atomic Absorption is the most accurate / popular Table from SVT

7 Atomic absorption method is well established and has a number of variations of light and measurement methods AAS is a relatively expensive method of measurement and required maintenance of vacuum windows and light source.

8 Two step processes involves varying the doping of Se and S into the CIG based structure to optimize performance TORREY HILLS TECHNOLOGIES, LLC

9 New low cost Sulphur & Selenium Sensor for vacuum deposition process measurement patent pending Argon injection point for high Se loads in the chamber dilutes the Se signal and prevents saturation of the sensor. Argon flow can be automatically regulated via Speedflo unit. 50 sccm MFC is included in the sensor package as standard can be removed on request KF25 or CF25 connection to the chamber Sulphur & Selenium sensor location CF40 with copper gaskets Heater jacket to prevent Se condensation from the chamber ensures Se in chamber is measured, not Se in the gauge area. Temperature is regulated automatically and powered via speedflo software

10 Sensitivity of the sensor change in voltage output against Se pressure in the vacuum chamber V (Se Sensor) p (x 10-6 mbar)

11 Sulphur & Selenium Sensor for vacuum non intrusive method of chemically measuring the Se level in a vacuum chamber Se pressure (x 10-6 mbar) Pressure gauge Se selective sensor t (s) Se sensor value (%) The SeS sensor mounted on the vacuum chamber wall specifically to measure the level of Se or S inside a vacuum chamber. It is a chemical type sensor that provides a voltage change as the Se level varies within the chamber. The above graph displays the variation of sensor signal in response to Se delivery variations from the PEC200 pulsed effusion cell. For these large Se variations, the sensor takes 1-2 minutes to reach the final concentration.

12 Comparing the Se sensor to a quartz crystal microbalance Se Deposition rate (nm/s) Quartz crystal monitor Se selective sensor t (s) Se sensor value (%) The selenium sensor is more sensitive & reliable than a quartz crystal monitor in sensing the changes in Se delivery.

13 Adjusting Se delivery by varying the pulse frequency of a Gencoa N4E pulsed effusion cell and 3 temp zone adjustment

14 Zn OES signal, V Se sensor signal, V Selenium Sensor DC sputtering of Zn Se cannot be seen in the change in the optical signal from the Zn sputtered species but can be measured by the sensor Zn ON Se OFF Z Zn ON Se ON Increase in Se - PEC200 valve opening pulse frequency Time, s 5.5 Zn (OES) Se sensor X

15 Combining Se sensing with pulsed Se delivery and Hipims sputtering of Zn Lower levels of Se delivery with variations

16 Higher levels of Se delivery

17 Se sensor can adapt to high or low Se system delivery by changing the amount of purge gas prevents sensor overload

18 Active feedback control changing set-points and controlling compositions at different levels for reactively sputtered CIGS 80 Cu rich S poor Cu poor S rich SetPoint (%) Sensor (%) Sensor (%) % 60% 40% 80% SetPoint Actuator (%) Actuator (%) Time(s)

19 Sulphur & Selenium Sensor for vacuum deposition process measurement and control - feedback control options Controller Voltage Out Actuator Options Se Flow Process (Speedflo) Voltage In PEC Pulse frequency (fast actuation), Mechanical valve position (medium), Effusion cell temperature (slow) (Thermal deposition, Vacuum selenization, Reactive Sputtering) S & Se Sensor Signal S or Se intensity A feedback controller will stabilise the process allowing for regulated S or Se delivery and reducing greatly the amount of S or Se used as well as accurate compositional control.

20 Sulphur & Selenium Sensor for vacuum deposition processes can be as a sensor only or with feedback control module The Speedflo controller interfaces with a PLC, OPC server or window s interface to display the signal and control the sensor functions. Feedback mode is also available via the Se delivery source to automatically regulate the Se at a certain level.

21 Sulphur & Selenium Sensor for vacuum deposition processes different ways to integrate the voltage output from the sensor SPF/M 2 sensor inputs & 3 outputs Ethernet TCP/IP Windows control interface dll / OPC SPF/M 8 sensor inputs & 8 outputs, i.e. can sense and control 8 different Se zones simultaneously S & Se sensor module Machine control

22 New device for Selenium and Sulphur sensing in a vacuum Conclusions There is a need to improve the performance of CIGS cells New manufacturing methods and technology is required A new type of low cost sensor for the measurement of Se and S in a vacuum chamber has been developed and demonstrated to give reliable measurements for a range of Se and S concentrations This SES sensor can improve the control of the deposition processes and reduce Se and S wastage currently as high as 90% wasted The widespread use of reliable low cost sensing technology can be a reality

23 Gencoa is actively combining technologies and developing ways to enhance thin film devices Thank you for your attention Thank You Please visit us at Booth 506 or