Epitaxial thin film silicon solar cells with CVD grown emitters exceeding 16% efficiency

Epitaxial thin film silicon solar cell technology, consisting of a thin high quality epitaxial layer on top of a highly doped low-cost silicon substrate, is one of the most promising midterm alternatives for cost effective industrial solar cell manufacturing. Currently, CVD is used to grow the active layer. However, besides the growth of the base, also the emitter can be grown by CVD, which allows the growth of almost any doping profile, designed as desired to optimize the emitter and base properties. A two step emitter with a highly doped top layer acting as a front surface field and a moderate doped bulk layer was designed and tested. Very sharp transitions between the different epi-layers boost the open-circuit voltage drastically up to values around 650 mV. However, the Jsc of those cells were limited to values around 29 mA/cm². To enhance the Jsc, light trapping methods are introduced to enhance the optical thickness of the 20 ¿m thick active base. In this paper, solar cell processes are established integrating both a CVD grown emitter, and state-of-the-art concepts for optical light trapping in epitaxial cells. In this way, the significant increase in Voc is combined with an improved short-circuit currents and leads to a record efficiency of 16.1% with a current density of 33.2 mA/cm², approaching the Jsc of bulk silicon solar cells.