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Industrial tunnel oxide and passivated contact (i-TOPCon) solar cells were metallized at Fraunhofer ISE using ultrashort pulse laser ablation of the passivation layers for the subsequent Ni/Cu/Ag plating process. The solar cells feature a tunnel SiO x and n-type doped polysilicon layer covered by a SiN x at the rear side, whereas the front side is made of a boron emitter passivated with a AlO x /SiN x stack. The reference i-TOPCon solar cells screen-printed at the supplier reach an efficiency of 23.46% measured by Fraunhofer ISE CalLab. The impact of the laser process on the implied open circuit voltage (iV oc ) is characterized showing minor impact on the TOPCon side, while the emitter side reveals an increased iV oc loss due to laser damage. Loss analysis by simulating the plated solar cells points out the benefit of reducing the laser contact opening (LCO) area in terms of shading and contact recombination.Optimization of laser ablation and hydrofluoric acid (HF) pretreatment process result in V oc > 700 mV and FF > 82% leading to a mean efficiency 23.6% measured in-house and a champion efficiency of 23.84% measured at Fraunhofer ISE CalLab thus outperforming the references by 0.4% abs .

We describe an erbium fiber laser that is passively mode locked by a novel, precision antireflection-coated semiconductor saturable-absorber mirror that incorporates an additional two-photon absorber. It is shown that passive mode locking evolves from a Q-switching instability. The results are achieved by use of saturable absorbers that provide a large (15%) nonlinear (saturable) loss. Exploiting two-photon absorption can substantially reduce the peak power of the Q-switched pulses, which results in improved reliability of the laser. Moreover, two-photon absorption can be used to produce an optimal stability range for saturable-absorber mode locking.

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