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.

Thanks to the excellent passivation, high conductivity, low parasitic absorption and simple process, the wide-bandgap doping-free carrier selective contacts have been attracting much attention. In this work, the wide-bandgap high work function of Al 2O 3/MoO x stacks were prepared using the low-temperature atomic layer deposition and thermal evaporation technique, respectively, and the interfacial evolution and the elements distribution were examined using high-resolution transmission electron microscopy coupled with energy-dispersive spectroscopy. The passivation and conductivity of the Al 2O 3/MoO x stacks were systematical investigated by varying their thicknesses. The high effective minority carriers lifetime of 513 μs and the low series resistance of 0.24 mΩ are realized on the 7nm-Al 2O 3/5nm-MoO x and 7nm-Al 2O 3/3nm-MoO x stacks, respectively. Benefiting from the excellent surface passivation and conductivity, the industrial size (182×185.3 mm 2) n-TOPCon solar cell with a total area front 7nm-Al 2O 3/3nm-MoO x stacks demonstrates a champion power conversion efficiency (PCE) of 24.48%, as well as a short-circuit current density of 41.06 mA cm −2, an open-circuit voltage of 721 mV, and a fill factor of 82.66%. This work provides an effective way to enable the PCE over 26.0% and lower the process temperature for TOPCon solar cells with doping-free carrier selective contacts.

In recent years, developing dopant-free carrier-selective contacts, instead of heavily doped Si layer (either externally or internally), for crystalline silicon (c-Si) solar cells have attracted considerable interests with the aims to reduce parasitic light absorption and fabrication cost. However, the stability still remains a big challenge for dopant-free contacts, especially when thermal treatment is involved, which limits their industrial adoption. In this study, a perovskite material ZnTiO 3 combining with an ultrathin (~1 nm) SiO 2 film and Al layer is used as an electron-selective contact, forming an isotype heterojunction with n-type c-Si. The perovskite/c-Si heterojunction solar cells exhibit a performance-enhanced effect by post-metallization annealing when the annealing temperature is 200-350 °C. Thanks to the post-annealing treatment, an impressive efficiency of 22.0% has been demonstrated, which is 3.5% in absolute value higher than that of the as-fabricated solar cell. A detailed material and device characterization reveal that post annealing leads to the diffusion of Al into ZnTiO 3 film, thus doping the film and reducing its work function. Besides, the coverage of SiO 2 is also improved. Both these two factors contribute to the enhanced passivation effect and electron selectivity of the ZnTiO 3-based contact, and hence improve the cell performance.