Thin SiO x interlayers are often formed naturally during the deposition of transition metal oxides on silicon surfaces due to interfacial reaction. The SiO x layer, often only several atomic layers thick, becomes the interface between the Si and deposited metal oxide and can therefore influence the electrical properties and thermal stability of the deposited stack. This work explores the potential benefits of controlling the properties of the SiO x interlayer by the introduction of pregrown high-quality SiO x which also inhibits the formation of low-quality SiO x from the metal-oxide deposition process. This work demonstrates that a high-quality pregrown SiO x can reduce the interfacial reaction and results in a more stoichiometric MoO x with improved surface passivation and thermal stability linked to its lower D it. Detailed experimental data on carrier selectivity, carrier transport efficiency, annealing stability up to 250 °C, and in-depth material analysis are presented.

Imaging In article number http://doi.wiley.com/10.1002/solr.202100348, Anh Dinh Bui, Daniel Macdonald, Hieu T. Nguyen, and co‐workers report a fast, non‐invasive, camera‐based method to image pseudo current density ‐ voltage curves of various perovskite‐based structures from partially finished to finished cells with micron‐scale spatial resolution. This approach is useful to resolve the inhomogeneity of implied open‐circuit voltage and maximum fill factor across the devices, and their evolution during degradation.

This work compares the firing response of ex‐situ doped p‐ and n‐type polysilicon (poly‐Si) passivating contacts and identifies possible mechanisms underlying their distinct firing behavior. The p‐type poly‐Si shows greater firing stability than n‐type poly‐Si, particularly at a higher firing temperature, which results in a substantial increase in the recombination current density parameter J0 from 9 to 96 fA/cm2 upon firing at 900°C for n‐type poly‐Si, in comparison to an increase from 11 to 30 fA/cm2 for p‐type poly‐Si. It is observed that p‐type poly‐Si contacts only suffer a slight degradation or even exhibit a small improvement in J0 after firing at 800°C, depending on the boron diffusion temperature. Secondary ion mass spectrometry (SIMS) results demonstrate that the hydrogen concentration near the interfacial SiOx increases with the peak firing temperature in n‐type poly‐Si, whereas the hydrogen profile remains unchanged for p‐type poly‐Si upon firing at various temperatures. Moreover, we observe that injecting additional hydrogen into the poly‐Si/SiOx stacks fired with SiNx coating layers further degrades n‐type poly‐Si, but recovers the J0 of p‐type poly‐Si to the value before firing. In contrast, removing hydrogen from the fired poly‐Si/SiOx stacks leads to an initial recovery and then a second degradation of J0 in n‐type poly‐Si, but no substantial impact on p‐type poly‐Si. It is hypothesized that the distinct difference in the firing impact on p‐ and n‐type poly‐Si is related to the different effective hydrogen diffusivity, which determines the hydrogen content surrounding the SiOx layer and hence the passivation quality after firing.

Polycrystalline‐silicon/oxide (poly‐Si/SiOx) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiOx interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly‐Si/SiOx structures. Herein, the factors that determine the blocking effects of the SiOx interlayers are identified and investigated by examining two general types of the SiOx interlayers: 1.3 nm ultrathin tunneling SiOx with negligible pinholes and 2.5 nm SiOx with thermally created pinholes. Iron is used as tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion‐limited segregation gettering model, the blocking effects of the SiOx interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiOx interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high‐temperature formation of the poly‐Si/SiOx structures, a SiOx interlayer that is less stoichiometric or with a higher pinhole density is preferred.

Metallic impurities in the silicon wafer bulk are one of the major efficiency-limiting factors in silicon solar cells. Gettering can be used to significantly lower the metal concentrations. Although gettering by silicon nitride films has been reported in literature, much remains unknown about its gettering behaviors and mechanisms. In this study, the gettering kinetics and mechanisms of silicon nitride films, from both plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD), are investigated. By monitoring the kinetics of iron loss from the silicon wafer bulk, it is confirmed that silicon nitride gettering takes place mainly via segregation, even at a low annealing temperature of 400 °C. Simulation of the gettering kinetics suggests the presence of an interfacial diffusion barrier in some cases, which slows down the transport of iron impurities from the silicon wafer bulk to the silicon nitride gettering regions. The activation energy of the segregation gettering process is estimated to be 0.9 ± 0.1 eV for the investigated PECVD silicon nitride film at 400–900 °C and 1.6 ± 0.5 eV for the investigated LPCVD silicon nitride film at 400–700 °C.