GaAs based thin film solar cells have great application value in military, aerospace and other fields.
Based on the conventional GaAs based solar cell epitaxial structure, an InGaP etch stop layer is inserted between the epitaxial layer and the GaAs substrate. Using MOCVD growth equipment to complete the epitaxial layer growth, solve the key growth technology of double junction cell, such as layer thickness and doping concentration, doping source diffusion, heterojunction, tunnel junction, uniformity and so on. It is compatible with the conventional GaAs based solar cell surface preparation process.
Compared with the GaAs substrate stripping process, the wet substrate removal process has less etching damage and less chemical residue on the surface of the bare epitaxial layer, which can obtain a cleaner and smoother epitaxial layer surface and improve the contact performance between the GaAs Solar cell bottom electrode and semiconductor materials. By optimizing the acid bright copper plating process, the uniformity, flatness, brightness and film stress of copper film were improved, and the ideal metal film substrate was obtained. Electroplating is an electrochemical deposition process in solution. Compared with the bonding process, it has no strict requirements on the cleanliness of the operating environment, and does not require the epitaxial layer to go through the process of high temperature and high pressure. Therefore, it can avoid the mechanical damage caused by surface particle residue or substrate warping, and effectively improve the uniformity and yield of products. Electroplating can flexibly adjust the thickness of the metal substrate, so that the thin film cell has good flexibility and bending characteristics, which has great advantages for the preparation of large area flexible thin film cell.
The total thickness of the thin film cell is only about 30 microns, which has the characteristics of ultra light and ultra-thin, showing high power to mass ratio and power to volume ratio. After multiple bending cycles, there is no obvious mechanical damage such as cracks and shedding. After up to 100 bending cycles, the performance degradation of double junction thin film cell is very small, showing good mechanical stability. Double junction thin film cell has strong photoluminescence (PL) and electroluminescence (EL) characteristics, especially the PL characteristics of cell chip under simulated light, which can be used as a quick means to test the material growth and device preparation process. The PL peaks of InGaP top cell and GaAs bottom cell are 648nm and 874nm respectively, which are excited by 532nm laser.