New Window Technology fo CIGS PV Cell

Purpose and goal

The aim of this project is the implementation and characterization of new window layer structures in CIGS solar cells and modules. A reduction of optical losses and an improved junction quality is expected to increase the module efficiency by up to 10% relatively. In combination with the application of cost-efficient chemical deposition methods, the price/Watt ratio for the final solar module can be significantly reduced. It is planned to achieve the project goals by designing a window layer stack that does not contain any toxic elements like for example cadmium.

Expected results and effects

A process for growth of ZnO:B TCO layers was transferred from Hanergy (China) to Solibro (Sweden). After an extended optimization period, the process is mature and the desired improvement in Jsc and also in FF is observed. However, the Voc is slightly decreased. Overall, the change of TCO leads to a 3% relative increase in efficiency with the additional benefit that the costs/Watt ratio for module production will decrease. The high potential of In2O3:H TCO layers was proven on a laboratory scale. Corresponding results were published in several scientific journals.

Planned approach and implementation

A large scale CVD tool for ZnO:B films was installed and evaluated at Solibro Research AB. It is in operation and capable of coating full scale CIGS modules with a sufficient lateral homogeneity. In the medium term it is planned to transfer the TCO process from the conventional sputtered ZnO:Al to CVD ZnO:B and to apply it in standard production. Well-developed In2O3:H processes (sputtering and ALD) are available at Uppsala University to continue studying the potential of next generation TCOs. ALD buffer layer development is ongoing for CIGS surfaces treated with alkali salts.