Micro-Scale III-V/Ge Multijunction Solar Cell with Through Cell Via Contacts

There has been a growing interest for micro-scale concentrator photovoltaics (micro-CPV) over the past few years. The main goal is to reduce the cell size to a sub-millimetric range to gain several benefits such as better handling, better thermal management and reduced series resistance losses. In this work, we present the microfabrication of micro-scale III-V/Ge triple junction solar cells with through cell via contacts (TCVC) for micro-CPV applications. This contact architecture transfers the front side contact to the back side by using isolated and metallized vias to reduce the shading and the resistive losses. A process was developed to fabricate 180x180 µm2 solar cells with a single through cell via contact. The first prototypes have been successfully fabricated and the electrical characterization shows good performance. A 1-sun open-circuit voltage of 2.28 V was obtained, which is high considering the small device size and the high perimeter-to-area ratio (232cm-1). This new architecture represent a key improvement for micro-scale solar cells. With standard busbar and grid line contacts, the metallized area to device area ratio keeps increasing as the device size is reduced. This reduces the power yield per wafer and hinders the benefits of micro-CPV. With TCVC, the metallization ratio remains the same (2.8 ^% ), regardless of the device size. As a result, this new architecture could increase the wafer area yield by up to 267% for 180x180 µm2 solar cells.