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Hydrogenation is a crucial step for improving the efficiency of multicrystalline silicon solar cells. In this work, we investigate the influence of different firing and annealing conditions on the efficacy of bulk hydrogenation in state‐of‐the‐art high‐performance multicrystalline silicon, for a range of hydrogen‐containing dielectric layers. All of the dielectric films studied, including aluminium oxide, amorphous silicon, and silicon nitride deposited with different tools, yield similar bulk lifetimes when annealed at optimal conditions. However, the optimal conditions vary between films, depending on the film properties. The overall hydrogenation effect does not appear to be affected by the cooling rate used during firing or by the application of illuminated annealing, performed at 250 ° C under 8 sun illumination. Moreover, we monitor in situ changes in the recombination behaviour of grain boundaries during the hydrogenation process, using a micro‐photoluminescence spectroscopy system with a temperature controlled stage. It is found that the hydrogenation reaction occurs at the annealing temperature range between 400 ° C and 500 ° C. [ABSTRACT FROM AUTHOR]

Herein, posttreatment techniques of phosphorus‐doped poly‐Si/SiOx passivating contacts, including forming gas annealing (FGA), atomic layer deposition (ALD) of hydrogenated aluminum oxide (AlOx:H), and plasma‐enhanced chemical vapor deposition (PECVD) of hydrogenated silicon nitride (SiNx:H), are investigated and compared in terms of their application to silicon solar cells. A simple FGA posttreatment produces a significant increase in the implied open circuit voltage (iVoc) and the effective minority‐carrier lifetime (τeff) of high‐resistivity crystalline Si (c‐Si) samples, whereas low‐resistivity samples show a minimal change. Treatment by means of AlOx:H and/or SiNx:H followed by postdeposition FGA results in a universal increase in τeff and iVoc for all substrate resistivities (as high as 12.5 ms and 728 mV for 100 Ω cm and 5.4 ms and 727 mV for 2 Ω cm n‐type c‐Si substrates). In addition, both the FGA and AlOx:H + FGA techniques can inject sufficient hydrogen into the samples to passivate defects at the SiOx/c‐Si and poly‐Si/SiOx interfaces. However, this hydrogen concentration is insufficient to neutralize both the nonradiative defects inside the poly‐Si films and dangling bonds associated with the amorphous Si phase present in them. The hydrogen injected by the SiNx:H + FGA technique can passivate both the interfaces and the defects and dangling bonds within the poly‐Si film. These results are confirmed by low‐temperature photoluminescence spectroscopy, Fourier transform infrared spectroscopy, and dynamic secondary‐ion mass spectrometry measurements. [ABSTRACT FROM AUTHOR]

Abstract: When measured at low temperature (79 K), the photoluminescence (PL) spectra from silicon wafers containing a diffused heavily doped layer exhibit a second peak due to band gap narrowing in the diffused region. This work aims to decompose this peak into components arising from the various doping concentrations within the diffused layer. Whilst the peak position of silicon band‐to‐band PL spectra changes significantly with the doping concentration in silicon, the shape of the spectra also varies strongly with doping concentrations due to the broadening effects of band‐filling and band‐tail states. By measuring PL spectra on a range of uniformly heavily doped wafers, we show that these changes in spectral position and shape can be accurately modelled for doping concentrations above 1 × 1019 cm−3 using simple parameterisations, with minimal impact of variations in excitation intensity or injection level. This allows the PL spectra for a range of arbitrary doping concentrations to be reconstructed. We then show that the PL spectra from a thermally boron‐diffused wafer, in which the boron concentration changes with depth, can be reconstructed based on a superposition of PL spectra arising from the layers of different doping beneath the surface. Furthermore, the scaling factor for each layer can be accurately estimated based on the doping profile and the fraction of incident light absorbed in the layer. [ABSTRACT FROM AUTHOR]

We report and explain the photoluminescence spectra emitted from silicon solar cells with heavily-doped layers at the surface. A micro-photoluminescence spectroscopy system is employed to investigate the total spectrum emitted from both the heavily-doped layer and the silicon substrate with micron-scale spatial resolution. The two regions of the device give rise to separate photoluminescence peaks, due to band-gap narrowing effects in the highly-doped layer. Two key parameters, the absorption depth of the excitation wavelength, and the sample temperature, are shown to be critical to reveal the separate signatures from the two regions. Finally, this technique is applied to locally diffused and laser-doped regions on silicon solar cell pre-cursors, demonstrating the potential value of this micron-scale technique in studying and optimizing locally doped regions. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Micro-photoluminescence spectroscopy is applied in this work to characterise the shallow phosphorus diffusions occurring below poly-silicon passivating contacts for silicon solar cells, courtesy of the bandgap narrowing effect in the heavily-doped region. We present the photoluminescence spectra from samples of various diffusion profiles, achieved by changing the phosphorus diffusion temperature and oxide interlayer thickness. The photoluminescence peak from the shallow phosphorus diffusion region, when normalised against the substrate crystalline silicon peak, changes in intensity in accordance with the dopant profiles. Photoluminescence spectra measured with two lasers of different penetration depths are compared in this study, and their relative strengths and weaknesses are assessed. Micron-scale line scanning across localised poly-silicon structures demonstrates that the method can identify the presence of the underlying diffused regions with a spatial resolution of several microns. • Proof of concept for using spectral photoluminescence to study the shallow diffusion underneath the passivating contact. • Exploring the sensitivities of photoluminescence intensities towards changes in the diffusion profile. • Discussion on the range of detection of photoluminescence as compared to optimised poly-silicon cell parameters. • Demonstrating the line scan from micro-photoluminescence systems in discovering localised features of passivating contacts. [ABSTRACT FROM AUTHOR]

Tandem Solar Cells: Spatially and Spectrally Resolved Absorptivity: New Approach for Degradation Studies in Perovskite and Perovskite/Silicon Tandem Solar Cells (Adv. In article number 1902901, Hieu T. Nguyen and co-workers employ spectrally and spatially resolved absorptivity at sub-bandgap wavelengths of perovskite materials, extracted from their luminescence spectra, to study degradation across perovskite and perovskite/silicon tandem solar cells. Absorptivity, degradation, perovskite, photoluminescence, tandem. [Extracted from the article]

Instability in perovskite solar cells is the main challenge for the commercialization of this solar technology. Here, a contactless, nondestructive approach is reported to study degradation across perovskite and perovskite/silicon tandem solar cells. The technique employs spectrally and spatially resolved absorptivity at sub‐bandgap wavelengths of perovskite materials, extracted from their luminescence spectra. Parasitic absorption in other layers, carrier diffusion, and photon smearing phenomena are all demonstrated to have negligible effects on the extracted absorptivity. The absorptivity is demonstrated to reflect real degradation in the perovskite film and is much more robust and sensitive than its luminescence spectral peak position, representing its optical bandgap, and intensity. The technique is applied to study various common factors which induce and accelerate degradation in perovskite solar cells including air and heat exposure and light soaking. Finally, the technique is employed to extract the individual absorptivity component from the perovskite layer in a monolithic perovskite/silicon tandem structure. The results demonstrate the value of this approach for monitoring degradation mechanisms in perovskite and perovskite/silicon tandem cells at early stages of degradation and various fabrication stages. [ABSTRACT FROM AUTHOR]

A fast, nondestructive, camera‐based method to capture optical bandgap images of perovskite solar cells (PSCs) with micrometer‐scale spatial resolution is developed. This imaging technique utilizes well‐defined and relatively symmetrical band‐to‐band luminescence spectra emitted from perovskite materials, whose spectral peak locations coincide with absorption thresholds and thus represent their optical bandgaps. The technique is employed to capture relative variations in optical bandgaps across various PSCs, and to resolve optical bandgap inhomogeneity within the same device due to material degradation and impurities. Degradation and impurities are found to both cause optical bandgap shifts inside the materials. The results are confirmed with micro‐photoluminescence spectroscopy scans. The excellent agreement between the two techniques opens opportunities for this imaging concept to become a quantified, high spatial resolution, large‐area characterization tool of PSCs. This development continues to strengthen the high value of luminescence imaging for the research and development of this photovoltaic technology. A fast, nondestructive, camera‐based method to capture optical bandgap images of perovskite solar cells with micrometer‐scale spatial resolution is developed. This technique allows for the probing of relative variations in optical bandgaps across various solar cells, and for the resolution of bandgap inhomogeneity within the same device due to material degradation and impurities. The results are independently confirmed with other optical‐based techniques. [ABSTRACT FROM AUTHOR]

In article number 1802790, Daniel Macdonald, Hieu T. Nguyen, and co‐workers develop a fast, non‐destructive, camera‐based method to capture optical bandgap images of perovskite solar cells with micron‐scale spatial resolution. This technique allows them to probe relative variations in optical bandgaps across various solar cells, and to resolve optical bandgap inhomogeneity within the same device due to material degradation and impurities. The results are independently confirmed with other optical‐based techniques. [ABSTRACT FROM AUTHOR]

In this study, we explore the utilization of inkjet printing technology with liquid ink to fabricate boron-doped polycrystalline silicon (poly-Si)/SiO x passivating contacts. The impacts of substrate morphology, baseplate temperature, and surface oxide on the printing performance were investigated to achieve distinct printed patterns. Moreover, a pre-oxidation process at 750 °C for 30 min was conducted as a strategy to prevent dopant spreading from the printed pattern via the gas phase during the high-temperature annealing. Thereafter, the influences of annealing temperature on the formed poly-Si passivating contact quality were studied. By applying optimized process conditions on intrinsic poly-Si(i-poly-Si)/SiO x /p-type crystalline Si (c-Si) substrates, promising surface passivation was achieved with an implied open-circuit voltage (i V oc) of 718 mV and a low contact resistivity (ρ c) of 6.1 mΩ cm2 after annealing at 950 °C followed by a hydrogenation treatment. Optical images demonstrate that single-droplet dopant lines with a width of 69 μm could be realized on a mechanically polished substrate by printing with a drop spacing of 40 μm, while the line width expands on rough surfaces or when printing with a reduced drop spacing. Furthermore, high-resolution micro-photoluminescence maps clearly illustrate the localization of the boron-doped regions on polished and planar substrates after annealing. We also realized the formation of localized inkjet-printed phosphorus- and boron-doped poly-Si passivating contacts simultaneously within a single annealing step at 950 °C. These findings underscore the potential of inkjet printing as a promising technique for fabricating localized poly-Si/SiO x passivating contacts in high-efficiency silicon solar cells. • Application of inkjet printing for localized doping of poly-Si passivating contact. • i V oc of 718 mV and ρ c of 6.1 mΩ cm2 were achieved for p-type poly-Si contact. • Pre-oxidation process mitigated unwanted dopant spreading during N 2 annealing. • μPL map shows 69 μm wide localized poly-Si passivating contacts. • Simultaneous formation of localized n- and p-type poly-Si passivating contacts. [ABSTRACT FROM AUTHOR]

This paper describes the influence of plasma enhanced chemical vapor deposition (PECVD) deposition temperature on heavily doped silicon based (doped-Si/SiO x) passivating contacts for silicon solar cells. The doped-Si films are obtained by PECVD intrinsic amorphous silicon (a-Si) and a subsequent thermal POCl 3 diffusion process. By changing the deposition temperature of PECVD, a-Si films with different degrees of crystallinity and density can be obtained. These differences between the a-Si films result in different properties of the passivating contacts in terms of passivation quality and carrier selectivity. By exploring a range of PECVD deposition temperatures from 250 °C to 470 °C, the best passivation quality is obtained at a temperature of 420 °C. On the other hand, the contact resistivity decreases with increasing deposition temperature. After studying the a-Si properties and the resulting passivating contact properties, we obtain optimal passivating contacts with a high implied open-circuit voltage (iV oc) of 742 mV and a low contact resistivity ρ c of 6.4 mΩ∙cm2. • The influence of different PECVD deposition temperatures on passivating contacts is investigated. • The relationship between material properties and final passivating contact performance is established. • Excellent passivation and contact resistance are obtained. [ABSTRACT FROM AUTHOR]

Among common methods to form polycrystalline silicon (poly-Si) films for passivating-contact solar cells, physical vapor deposition, in particular sputtering, is the safest one as it does not require any toxic gaseous precursors. One of the critical parameters to control the properties of sputtered silicon films is their deposition pressure. In this work, structural and optoelectronic characteristics of ex-situ boron-doped poly-Si/SiO x passivating contacts, formed from sputtered intrinsic amorphous silicon (a-Si) deposited at different pressures on top of SiO x /c-Si substrates and subjected to a high-temperature boron diffusion step, are investigated. The deposition rate and density of the as-deposited a-Si films increase with reducing pressure. Low-temperature photoluminescence spectra captured from the as-deposited samples at different pressures do not show typical emissions from hydrogenated a-Si. Meanwhile, their Fourier-transform infrared absorption spectra all show Si–H stretching modes, indicating that hydrogen had been initially incorporated into the chemical SiO x layers and eventually hydrogenated the a-Si/SiO x interfaces during the sputtering process. After the high-temperature boron-diffusion step, all hydrogen-related peaks disappear. Lower pressure films (1.5 and 2.5 mTorr) show more consistent improved performance after hydrogen treatments, compared to higher pressure films (4 and 5 mTorr). The resultant passivating contacts at 2.5 mTorr achieve a low single-side recombination current density J o of ~9 fA/cm2, whereas their contact resistivity is still low at 15 mΩ cm2. • Effects of sputtering pressure on the structural and optoelectronic properties of the as-deposited a-Si films and their corresponding ex-situ boron-doped poly-Si/SiO x passivating contacts were investigated. • The Si–H stretching modes observed by FTIR in the as-deposited films are likely a consequence of residual hydrogen incorporated to the oxide layer during its chemical growth. • The resultant poly-Si/SiO x contacts show a reasonably good initial passivation quality with J o of 24 fA/cm2 at 2.5 mTorr, which improves to 9 fA/cm2 after hydrogenation treatments. [ABSTRACT FROM AUTHOR]