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The power conversion efficiency of solar cells is strongly impacted by an unwanted loss of charge carriers occurring at semiconductor surfaces and interfaces. Here the use of ion‐charged oxide nanolayers to enhance the passivation of silicon surfaces via the field effect mechanism is reported. The first report of enhanced passivation from rubidium and cesium ion‐charged oxide nanolayers is provided. The charge state and formation energy of ion‐charged silicon dioxide are calculated from first principles. Ion embedding is demonstrated and exploited to control the interface population of carriers and minimize electron‐hole pair recombination. The passivation quality directly improves with charge concentration, yet excess ions can produce detrimental interface states. An optimal ionic charge concentration of ≈1.5 × 1012 q cm−2 is deduced, and a recombination velocity and current density as low as 2.8 cm s−1 and 7.8 fA cm−2 are achieved at the Si‐SiO2 interface. Maximized charge is shown to provide efficiency improvements as high as 0.7% absolute. This work provides a unique route to enhance passivation without compromising the film synthesis, thus retaining the antireflection and hydrogenation film properties. As such, ion‐charged dielectrics provide complementary paths for surface and interface optimization in future single‐junction and tandem solar cells. [ABSTRACT FROM AUTHOR]

The production and performance of p‐type inversion layer (IL) Si solar cells, manufactured with an ion‐injection technique that produces a highly charged dielectric nanolayer, are investigated. It is demonstrated that the field‐induced electron layer underneath the dielectric can reach a dark sheet resistance of 0.95 kΩ sq−1 on a 1 Ω cm n‐type substrate, lower than any previously reported. In addition, it is shown that the implied open‐circuit voltage of a p‐type IL cell precursor with a highly charged dielectric is equivalent to that of a cell with a phosphorous emitter. In the cell precursor, light‐beam‐induced current measurements are performed, and the uniformity and performance of the IL is demonstrated. Finally, simulations are used to explain the physical characteristics of the interface leading to extremely low sheet resistances, and to assess the efficiency potential of IL cells. IL cells are predicted to reach an efficiency of 24.5%, and 24.8% on 5/10 Ω cm substrates, by replacing the phosphorous emitter with a simpler manufacturing process. This requires a charge density of beyond 2 × 1013 cm−2, as is demonstrated here. Moreover, IL cells perform even better at higher charge densities and when negative charge is optimized at the rear dielectric. [ABSTRACT FROM AUTHOR]

Minimising charge losses at silicon interfaces is a major development area for highly efficient solar cells. Here we report on the interface improvements achieved by establishing a surface electric field during low-temperature firing of dielectric thin films. By inducing a corona electric field on the surface of a thin film stack, we observe significant modifications to the silicon-dielectric interface upon annealing, which correlate with the characteristics of interface defects. The passivation properties of the interfaces strongly depend on the polarity and strength of the electric field during firing, as well as the dielectric materials in the layer stack. We show that the surface electric fields not only influence surface carrier population but also affect the resulting chemical interface properties post-annealing. It is postulated that hydrogen migration plays a role in these observed effects. Leveraging the corona-induced electric field enables fine-tuning of both the chemical and field-effect passivation in thin film surface dielectrics, resulting in recombination current densities as low as 2.8 fA cm−2 in research-grade float zone silicon, and 14 fA cm−2 in industrial-grade textured silicon. The simplicity and versatility of the thin film electric polarisation enable a new strategy for controlling and exploiting the chemical enhancement of interfaces in solar cell devices, from current TOPCon and PERC devices to future multijunction silicon-based cells. • Hydrogen passivation from dielectrics is central to improving silicon solar cell performance. • Charge-assisted field effect passivation not only controls carrier population, but also affects interface chemistry. • Chemical passivation of Si-SiO 2 -SiN x interfaces depends on the polarity and strength of the surface electric field. • Optimal processing requires control of surface electric fields, chemical interface, hydrogenation and charge migration. • Understanding the interplay of hydrogen and electric fields is crucial for optimising silicon solar cell performance. [ABSTRACT FROM AUTHOR]

The Si–SiO 2 interface has and will continue to play a major role in the development of silicon photovoltaic devices. This work presents a detailed examination of how charge at or near this interface influences device performance. New understanding is identified on the effect of charge-induced potential fluctuations at the silicon surface. Such fluctuations have been considered in Si–SiO 2 recombination models previously, where a universal value of electrical potential deviation was used to represent the effect. However, the approach disregards that the variation occurs in the charge concentration rather than the potential. We modify the models to accurately reflect fluctuations in external charge, allowing a precise representation of surface recombination velocity, with self-consistent D i t , σ p , and σ n parameters. Correctly accounting for these parameters can provide insights into the passivation mechanisms which can aid the development of future devices. Using the corrected model, we find that the effect of charge fluctuation at the Si–SiO 2 interface is significant for the depletion regime to the weak inversion regime. This indicates that surface passivation dielectrics must operate with charge concentrations in excess of 2x1012 q/cm2 to avoid these effects. TCAD device simulations show that the efficiency of future PERC cells can improve up to 1% absolute when optimally charged dielectric coatings are applied both at the front and rear surfaces. [ABSTRACT FROM AUTHOR]

Dielectric-silicon interfaces are becoming ever more important to device performance. Charge inside a surface dielectric layer is neutralized in Si leading to an accumulation or inversion layer of free carriers. Additionally, states at the interface are occupied by charges via Shockley-Read-Hall carrier statistics. It is accepted that the density of interface charge near midgap, which can only reach a concentration as high as the density of states, D it , has a minor effect on band bending compared to the charges in the dielectric for a well passivated interface. Here, we show that it is the state density near the band edge what plays the major role. We conclude this by comparing our measurements with device modelling of a Si/SiO 2 interface. We measure the wafer sheet resistance while applying various amounts of positive charge to the passivating dielectric on an n-type Si wafer, and then reproduce the measured resistance values using simulations. This modelling indicates that D it at midgap has indeed a minor effect on sheet resistance change, while the total amount of tail states has a significant impact on the distribution of induced carriers. We test this model to detect the amount of acceptor-like states at the band-tails of oxide passivated silicon with different processing. We discuss and analyse the limitations of this technique. While we report on the Si/SiO 2 interface due to its relevance in photovoltaics, our method can be used to study the properties of other semiconductor-dielectric interfaces. As such this work is of importance across various optoelectronic devices. • Band tails interface state density is crucial to the charge carriers induced via field effect. • The sheet resistance of field induced layers strongly depends on D it at band tails. • Measurements and simulations of resistance allow the detection of D it at band tails. • This method can shed light in the carrier population control at device interfaces. [ABSTRACT FROM AUTHOR]