Al-based front contacts for HCPV solar cell

• Main Authors: Huo, Pengyun, Rey-Stolle, Ignacio
• Format: Conference Proceeding
• Language: English
• Subjects: Aluminum; Bilayers; Concentrators; Contact resistance; Critical components; Diffusion barriers; Diffusion layers; Electromigration; Germanium; Gold; Interdiffusion; Low cost; Metal sheets; Palladium; Performance enhancement; Photovoltaic cells; Resistance; Silver; Solar cells; Titanium
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.5001426

One of the key design challenges for high efficiency concentrator solar cells is to minimize the impact of ohmic losses associated with the large current densities that these devices handle. Typically, the most critical component of the series resistance is that of the front contact. On the one hand, in order to minimize its metal-semiconductor specific contact resistance, AuGeNi alloys are frequently used at the interface. On the other hand, to minimize the metal sheet resistance in the grid, thick silver layers are used, sometimes even coated with a gold capping layer. Such configuration results in a contact with good performance, but with elevated cost, and sometimes prone to suffering from degradation problems (electromigration, spiking, …) and deteriorated metal sheet conductance due to the interdiffusion between GaAs and the metals in the contact. In this work, we have explored a low cost high performance alternative based on Pd/Ge/Ti/Pd/Al metal stacks. The thicker top Al layer offers low metal resistivity, low cost, and good bondability; the middle Ti/Pd bilayer works as an efficient two-way diffusion barrier; and the interfacial Pd/Ge layer provides very low specific contact resistance to the GaAs contact layer. The results show that a Pd/Ge/Ti/Pd/Al front contact reduces the series resistance and thus can improve the performance of solar cells at ultrahigh concentration levels.