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Industrial mass production of solar cells is at a transition towards carrier selective junction solar cells with passivating contacts such as TOPCon, POLO or HJT. At the same time many manufacturers consider switching from p-type Cz-Si to n-type Cz-Si wafers. This contribution indicates that Ga-doped p-type Cz-Si material is still a viable option for the new type of devices while giving an opportunity to benefit from lower wafer cost. We report minority carrier diffusion lengths that are an order of magnitude larger than the thickness of the studied HJT and TOPCoRE devices. Stability aspects for operation in the field are discussed. Best TOPCoRE solar cells on Ga doped CZ-Si show a 0.2% higher efficiency than their co-processed n-type counterparts.

In 1997, a visionary study addressed limitations of the cost reduction potential for high efficiency solar cell devices. The results of this study triggered increased efforts for the development of production technology at Fraunhofer ISE. Many new approaches with substantial impact have been developed to the demonstration level. Economic analysis and a technology readiness terminology have been established to aid in assessing technological approaches, while the set-up of the PV technology evaluation center (PV-TEC) allowed for testing equipment, processes and materials on a higher maturity level. Reference processes building the backbone of the technology have been developed consistently further and device efficiencies follow a roughly 0.5%/a progress gradient since 2005, which is in good agreement with reports for an industrial pilot line. Today, we can rely on reference processes for PERC, TOPCon and SHJ in the PV-TEC with total and large area efficiencies of up to 22.7%, 24.0% and 24.1%, respectively. Further learning includes that for production technology R&D for PV devices high average power conversion efficiencies must be targeted and that scaling should be combined with thorough testing of products along the value chain. All cost and value determining parameters like production efficiency distribution, yield, capital and operational expenditure as well as degradation and performance under field conditions have to be monitored.

The authors present their work on laser-enhanced contact optimization (LECO) on iTOPCon solar cells. LECO improves the metal-semi-conductor contact resistivity ρc on the boron emitter and the n-TOPCon side from an underfired (thermal budget too low) state of 2.9 and 14.1 mΩcm2 to an enhanced state of 1.8 and 2.9 mΩcm2. Therefore, it enables the reduction of the optimal peak firing temperature, which leads to a decrease of metal induced recombination mainly on the boron emitter side and to minor degree on the n-TOPCon side, as shown in this work. Ultimately, LECO improves iTOPCon solar cells conversion efficiency by 0.6%abs compared with the optimal fired, untreated reference. Submitting those cells to 140°C and 2 suns equivalent irradiation for more than 4 h shows no impact on the conversion efficiency or any sign of light and elevated temperature-induced degradation (LeTID). Confirmed by ISE CalLab, LECO improved iTOPCon solar cells reach 23.8% and 24.1% conversion efficiency on industrial typical wafer formats and processes.

Industrial mass production of solar cells is moving towards carrier selective junction solar cells with passivating contacts such as TOPCon, POLO and HJT solar cells. At the same time many manufacturers consider switching from p-type Cz-Si to n-type Cz-Si wafers. This contribution indicates that Ga-doped p-type Cz-Si material is still a viable option for the new type of devices while giving an opportunity to benefit from 8-10% lower wafer cost. In that respect a Ga-doped Cz-Si ingot has been specified and characterized. We report minority carrier diffusion lengths that are an order of magnitude larger than the thickness of the studied HJT and TOPCoRE devices. So far best p-type HJT solar cells perform 0.2 % absolute lower in efficiency than co-processed n-type reference HJT solar cells. Best TOPCoRE solar cells on Ga doped Cz-Si, however, show a 0.2% to 0.3% higher efficiency than their co-processed n-type TOPCon counterparts.