Co-Diffused Back-Contact Back-Junction Silicon Solar Cells without Gap Regions

Abstract

In this paper, first generation back-contact backjunction (BC-BJ) silicon solar cells with cell efficiencies well above η = 20% were fabricated. The process sequence is industrially feasible, requires only one high-temperature step (codiffusion), and relies only on industrially available pattering technologies. The silicon-doping is performed from pre-patterned solid diffusion sources, which allow for the precise adjustment of phosphorus-and boron-doping levels. Based on the investigated process technologies, BC-BJ solar cells with gap and without gap between adjacent n + -and p + -doped areas were processed. On the one hand, a strong reduction of the process effort is possible by omitting the gap regions. On the other hand, parasitic tunneling currents through the narrow space charge region may occur. Hence, deep doped areas were realized to avoid tunneling currents in gap-free BC-BJ cells. This paper finishes with a detailed characterization of the manufactured cells including important cell measurements like I-V, SunsVOC, quantum efficiency, and an analysis of the cell specific fill factor losses.

Passivating boron silicate glasses for co-diffused high-efficiency n-type silicon solar cell application

“…Aside from commonly used gasphase diffusions using BBr 3 2,3 or BCl 3 4 sources, chemical vapor deposited (CVD) doping layers can be used to form the necessary diffusion source. [5][6][7][8][9][10] Using plasma-enhanced chemical vapor deposited (PECVD) doping layers [5][6][7][8][9][10] reduces the number of solar cell process steps compared to gas phase based processes and increases the flexibility of future industrial process flows for advanced cell designs such as n-type passivated emitter rear totally diffused (PERT) or interdigitated back contact (IBC) solar cells. 10 Furthermore, PECVD doping layers allow for a larger parameter range of doping profiles because of the separation of doping source deposition and drive-in step.…”

“…These layers have doping as well as barrier properties. 6,[8][9][10] CVD as well as gas-phase grown doping layers as diffusion source have not been commonly used as passivation layers, and CVD SiO x doping layers have not yet been reported to reach the high level of passivation and optical transmission necessary for good cell performance directly after the diffusion process without further treatment. In addition, related investigations on passivation of B containing SiO x layers did not show sufficiently low j 0E values for B emitters (depending on sheet resistance) up to now.…”

Simplified process for high efficiency, self-aligned IBC c-Si solar cells combining ion implantation and epitaxial growth: Design and fabrication

“…The process allows to define the BSF and emitter regions on the rear side with a gap in between by using only one photolithograph step. The gap region between the BSF and emitter avoids possible junction tunnelling recombination currents occurring when a direct contact between these two heavily doped regions is present [33,34]. In addition, the presented process exhibits a thermal budget up to 900°C and uses only two lithographic steps, which can be both replaced by screen printing or laser patterning processes at industrial level.…”

Analysis of n-type IBC solar cells with diffused boron emitter locally blocked by implanted phosphorus

“…Interdigitated back-contact (IBC) solar cells have a very high efficiency potential [1][2][3] but typically come along with a complex fabrication process [4]. One promising approach to simplify the process sequence is the combination of ion implantation and furnace diffusion to form the differently doped regions [5] which is depicted in Fig.…”