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, Dit, 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/SiO2 interface. We measure the wafer sheet resis-tance 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 Dit 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 tech-nique. While we report on the Si/SiO2 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.

This work investigates 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. We demonstrate that the field‐induced electron layer underneath the dielectric can reach a dark sheet resistance as low as 0.95 kΩ/sq on a 1 Ωcm n‐type substrate, lower than any previously reported. Additionally, we show 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 IL cell precursor we perform light beam induced current measurements and demonstrate the uniformity and performance of the inversion layer. Lastly, we use TCAD simulations 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 Ωcm substrates, by directly replacing the phosphorous emitter with a simpler manufacturing process. This requires a charge density in excess of 2x10¹³ cm‐2, as is demonstrated here. Moreover, IL cells perform even better at higher charge densities and when negative charge is optimised at the rear dielectric. This article is protected by copyright. All rights reserved.

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, ΔE C /ΔE V , 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 ΔE C /ΔE V 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.

In this work electron-beam-induced current (EBIC) is used to study the collection efficiency of emitters in in- dustrial silicon solar cells. Laser-doped local emitters have been deployed industrially, yet in mas production they are designed wider than the screen-printed silver fingers to allow alignment tolerances. EBIC has allowed to image and quantify the laser-induced damage that occurs in these local emitter regions. A model is developed to account for such damage, so that losses in EQE could be quantified from the observed EBIC collection charac- teristics. The damaged regions present ~12% lower collection efficiency at short wavelength (300–500 nm) than the homogenous emitter. Sentaurus TCAD simulations reveal that eliminating such damage would improve cell efficiency by ~0.12%. Additional degradation is found in a region 1–2 μm wide adjacent to the silver fingers, which has not been detected before. It is also found that pulsed laser doping leads to ~15 μm long un-doped gaps, along the direction of laser movement. As laser doping becomes a key part of industrial cell fabrication, it is crucial to develop a better understanding of the potential pitfalls, and future improvements to the process. The versatility of EBIC imaging is also demonstrated using FIB milling to improve lateral resolution and study the depth profile of boron emitters in newly developed industrial i-TOPCon cells. EBIC imaging, in combination with advanced device simulations, have proven powerful tools to elucidate carrier collection characteristics and drawbacks, thus helping to understand and improve fabrication processes at industrial level.