Oerlikon Solar KAI 1200 System

Summary

With this innovation the Oerlikon Solar KAI 1200 PECVD system can deposit amorphous and microcrystalline absorber layers faster and at better quality resulting in a significant reduction of the production cost of silicon thin-film solar modules.

Description

The KAI 1200 production system has originally been used to produce TFT semiconductor devices in the LCD industry. All suppliers to this market around the globe have been using 13.56 MHz RF excitation frequency to generate the plasma. The same technology can be used to produce amorphous and microcrystalline solar cells. The biggest disadvantage of this type of production equipment at 13.56MHz though is the limited deposition rate. In the semiconductor industry a higher deposition rate is easily obtained by increasing the plasma power. On thin film silicon solar cells this is not an option as increasing the plasma power leads to a higher defect density in the silicon absorber material caused by the higher ion bombardment. On the solar device level this causes a stronger degradation, the so called light induced degradation. One of the most promising solutions to overcome this issue was to considerably increase the plasma frequency. Many Universities like the IMT in Neuchatel and thin-film solar cell producers like Mitsubishi Heavy industries or Uni-Solar have confirmed this mechanism that allows reaching higher deposition rates while maintaining or improving the absorber layer quality. The technical challenge was to increase the plasma frequency while at the same time avoiding the standing wave effect which strongly reduces the layer uniformity at large substrate size.

Innovation Aspect

With an innovative solution to overcome the standing wave effect Oerlikon Solar became the first company to commercially introduce a product with a 40MHz VHF plasma frequency for large scale PECVD deposition. Based on its research in partnership with the IMT in Neuchatel and the EPFL in Lausanne, a dielectric lens compensation was invented which eliminates the standing wave effect. From the first concepts in early 2000, Oerlikon Solar successfully implemented this new type plasma source into mass production. Since then over 800’000 thin-film silicon solar modules have been produced applying Oerlikon Solar’s 40 MHz technology.

Benefits

The 40 MHz VHF technology has considerably increased deposition rates and at the same improved the absorber layer quality. Where typical deposition rates of 1 to 2 Å/s were reported the novel dielectric lens allowed Oerlikon Solar to double the deposition rate on its 1.4m2 solar panels at best in class layer quality. Amorphous single junction modules have shown an initial aperture efficiency of 9.6%. The PECVD deposition of the absorber layer is the most critical and also the most costly production step in a production line for thin-film silicon solar modules. This innovation improved the cycle time for the deposition of the amorphous absorber layer by over 30% which was another major step in reducing the total cost of ownership on the path to grid parity.