Kaining Ding, Karsten Bittkau, Alexander Eberst, Andreas Lambertz, Uwe Rau, Forschungszentrum Jülich GmbH, Jülich, Germany
Silicon heterojunction (SHJ) solar technology has emerged as a frontrunner in the pursuit of efficient and cost-effective photovoltaic solutions. The years 2023/2024 have witnessed significant strides in this domain, marked by the continuous integration of advanced concepts into mass production. This contribution aims to provide a comprehensive overview of the advancements in SHJ technology through thin film innovations.
The most intuitive approach to overcome parasitic absorption in SHJ solar cell front layers is to work on the transparency of these layers especially in UV and blue wavelength range. The transparency of the transparent conductive oxide can be tuned in a small range by the choice of alloying material, oxygen content, doping concentration, and film thickness. The addition of oxygen or carbon into the silicon films giving rise to silicon alloys with larger optical bandgap has been tested intensively. Intrinsic amorphous silicon oxide or carbide were meant to substitute the intrinsic amorphous silicon passivation layer. Doped amorphous or nano-crystalline silicon oxide or carbide were investigated as alternative to doped amorphous or nano-crystalline silicon, respectively. Until now, the most successful development is the front side doped nano-crystalline silicon oxide which gave rise to absolute efficiency improvement of >0.4% in production average and hence an industry standard now. Its success lies in the self-assembled formation of a 3-dimensional crystalline silicon network embedded in an amorphous silicon oxide matrix. Another more radical approach is to merge the doped layer and the passivation layer into one functional layer with a lower total thickness.