Novel tandem passivated contact approach for high-efficiency industrial
TOPCon solar cells
Abstract
Passivating contact solar cells have gradually become the mainstream
cell technology due to their excellent performance, and further
improving the conversion efficiency has become a focus of subsequent
research. Typically, achieving excellent field-effect passivation and
low contact resistivity in doped polycrystalline silicon (poly-Si) solar
cells requires heavy phosphorus doping. However, this approach can lead
to a predicament where excessive phosphorus diffuses into the Si
substrate during annealing, causing recombination losses. To address
this challenge, a tandem passivation contact structure incorporating an
intrinsic amorphous silicon (a-Si ( i)) film within the
passivation layers is introduced to retard the diffusion of phosphorus
into the Si substrate. Comprehensive characterizations of the tandem
structure were carried out to delve into the underlying mechanisms of
films with the integrated a-Si ( i) layer, including simulations,
surface microscopy, active dopants profiling, crystallographic
structure, chemical bonding, elemental distribution, and electrical
properties. Simulations revealed that the inserted intrinsic layer
effectively counteracts the clustering of phosphorus atoms, leading to a
more even distribution during crystal growth. Furthermore, active dopant
profiles indicate the potential of the introduced a-Si ( i) layer
to tailor the in-diffused dopant profile. Microscopy investigations
revealed the occurrence of blistering when the a-Si ( i)
thickness exceeds 30 nm. Passivation and contact performances of TOPCon
solar cells were assessed as the a-Si ( i) thickness was varied.
Notably, optimal electrical properties were achieved with 20 nm a-Si (
i) thickness. At this thickness, the implied open-circuit voltage
( iV OC) of the hydrogenated lifetime sample was
promoted to more than 736.6 mV on the polished wafer, corresponding to
the lowest single-side saturation current density ( J
0) of 4.3 fA/cm 2. In addition, a low
contact resistivity of 1.4 mΩ·cm 2 was achieved. Based
on this tandem passivation contact structure, industrial-sized TOPCon
solar cells were fabricated, giving an average efficiency of 23.83%,
0.25% higher than that of the baseline counterparts on the production
line. The above results demonstrate the role of the a-Si ( i)
film as a buffer layer, retarding the diffusion of phosphorus into the
Si substrate and obtaining a better passivation effect. This enables us
to further tailor the doping profile for high-efficiency solar cells.
Our work thus highlights a promising strategy to improve the performance
of TOPCon solar cells and showcases its potential for implementation in
industrial manufacturing.