No abstract

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.

Passivating contacts, featuring dual functions of defect passivation at the semiconductor surface and extracting one type of charge carrier, are recognized as the key enabler in achieving high-efficiency Si solar cells. In particular, a dopant-free and full-area passivating hole contact is critical to replace the conventional rear structure that features a partial Si-metal contact design with insulator interlayers. Herein, titanium oxide (TiO x ) nanolayers (∼5 nm) grown by atomic layer deposition over the full area of the Si surface followed by metal capping such as Ag are shown to provide efficient passivation and hole extraction with high optical reflectivity at the rear of Si solar cells. The proof-of-concept solar cells with either a p- or an n-Si absorber demonstrate ∼20% efficiency, exhibiting a higher infrared response compared with the conventional rear structure. Photoluminescence and electrical measurements on different TiO x /metal bilayers revealed that the field-effect passivation mechanism plays a major role in device performance, exploiting the high-concentration negative charge (>1012 q cm–2) at the Si/TiO x interface and the high work function (≥4.6 eV) of the capping metal. The developed contact offers great potential for boosting the efficiency and simplifying manufacturing of commercial Si solar cells.

Fully exploiting the power conversion efficiency limit of silicon solar cells requires the use of passivating contacts that minimize electrical losses at metal/silicon interfaces. An efficient hole-selective passivating contact remains one of the key challenges for this technology to be deployed industrially and to pave the way for adoption in tandem configurations. Here, we report the first account of silicon nitride (SiNx) nanolayers with electronic properties suitable for effective hole-selective contacts. We use x-ray photoemission methods to investigate ultra-thin SiNx grown via atomic layer deposition, and we find that the band alignment determined at the SiNx/Si interface favors hole transport. A band offset ratio, ΔEC/ΔEV, of 1.62 ± 0.24 is found at the SiNx/Si interface for the as-grown films. This equates to a 500-fold increase in tunneling selectivity for holes over electrons, for a film thickness of 3 nm. However, the thickness of such films increases by 2 Å–5 Å within 48 h in cleanroom conditions, which leads to a reduction in hole-selectivity. X-ray photoelectron spectroscopy depth profiling has shown this film growth to be linked to oxidation, and furthermore, it alters the ΔEC/ΔEV ratio to 1.22 ± 0.18. The SiNx/Si interface band alignment makes SiNx nanolayers a promising architecture to achieve widely sought hole-selective passivating contacts for high efficiency silicon solar cells.

Dielectric thin films are a fundamental part of solid-state devices providing the means for advanced structures and enhanced operation. Charged dielectrics are a particular kind in which embedded charge is used to create a static electric field which can add functionality and improve the performance of adjacent electronic materials. To date, the charge concentration has been limited to intrinsic defects present after dielectric synthesis, unstable corona charging, or complex implantation processes. While such charging mechanisms have been exploited in silicon surface passivation and energy harvesters, an alternative is presented here. Solid-state cations are migrated into SiO2 thin films using a gateless and implantation-free ion injecting method, which can provide greater long-term durability and enable fine charge tailoring. We demonstrate the migration kinetics and the stability of potassium, rubidium, and caesium cations inside of SiO2 thin films, showing that the ion concentration within the film can be tuned, leading to charge densities between 0.1-10 x 1012 qcm-2. A comprehensive model of ion injection and transport is presented along a detailed investigation of the kinetics of alkali cations. Integrating ionic charge into dielectrics to produce controlled electric fields can enable new architectures where field effect is exploited for improved electron devices.