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A multifaceted characterization approach is proposed, aiming to establish a link between nanoscale electrical properties and macroscale device characteristics. Current–voltage (I–V) measurements are combined with admittance spectroscopy (AS) and deep‐level transient spectroscopy (DLTS) for the analysis of charge‐related performance losses with time‐of‐flight secondary‐ion mass spectrometry to complete the understanding of ionic motion in the device. This is applied to the study of surface treatment in perovskite solar cells, which implements several strategies to improve band alignment, perovskite grain growth, and chemical passivation. An increase of both open‐circuit voltage (Voc) and fill factor of respectively 90 mV and 11% is shown after surface treatment, with an absolute efficiency increase of 4%. AS measurements, coupled with a lumped elements model, rule out the impact of transport layers as the origin of the performance improvement, rather pointing toward a reduction in ionic resistance in the perovskite bulk. Analysis of the DLTS response yields an activation energy of 0.41 eV, which is likely related to the same ionic mechanism discovered with AS. Finally, both of these techniques enable to show that the surface treatment main contribution is to reduce ion‐related recombination of charge carriers. [ABSTRACT FROM AUTHOR]

Lithium fluoride (LiF) is currently a very popular dielectric material used as a passivation or transport layer in a variety of applications, especially in high-efficiency solar cells. Despite this, its conduction properties and interface behavior with silicon remain largely unexplored. In this work, a LiF metal–insulator–semiconductor (MIS) structure is fabricated and characterized, and its properties are compared to the well-understood aluminum oxide (Al2O3) MIS structure. First, a higher current density in LiF compared to Al2O3 is highlighted, as well as its PN junction-like behavior with n-type silicon (n-Si), being rather unconventional for a dielectric layer. C–V measurements showcase the likely presence of an interface defect, causing an increase in the apparent doping and a shift in the flatband voltage VFB by +70 meV. This defect is found to be of the acceptor type, which renders the interface fixed charge more negative and improves the field-effect passivation in the case of a negative Qf. Finally, a density of interface states D i t ≈ 2 × 10 11 cm − 2 eV − 1 was found for LiF/n-Si, which is a low value showing appropriate chemical passivation at the interface. Overall, this work enables us to shed more light on the interface properties of LiF on n-Si, which is an essential step toward its wider use in state-of-the-art solar cells and other silicon-based devices. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the tradeoff between process control and cost-effectiveness for PERL-type process flows is investigated. Three aspects are considered: (1) whether a surface pre-treatment (for example special cleans and/or oxidation) prior to the deposition of the Al2O3-based rear-side passivation stack has to be added to the flow; (2) the quantification of the impact on cell parameters of skipping the rear-side polishing and/or the Al2O3 deposition; and (3) the possibility of replacing Al paste with PVD Al for rear side metallization. It is found that: (1) SPM-like cleans or thermal oxidation prior to Al2O3 deposition are useful steps to guarantee a stable Al2O3-based passivation process. (2) The efficiency drops by more than 1% by skipping the polishing, but only ≈0.15% by removing the Al2O3 from the passivation stack. Therefore, while rear-side polishing appears to be a necessary step for PERC/PERL technologies, the insertion of Al2O3 in the passivation stack could be traded off for a reduced production cost, depending on the (company-specific) details of cost-calculations. (3) Replacing Al paste with PVD Al for rear side metallization results in a deteriorated reflectance. The effect is larger for thinner passivation stacks. Although less advantageous in term of material costs with respect to PVD Al, screen-printed Al would therefore be the preferred choice for PERL cells featuring thin passivation stacks. [Copyright &y& Elsevier]

Poly-Si/SiO x passivating contacts enable the manufacturing of highly-efficient Si solar cells, but their fabrication commonly relies on an extra high-temperature process such as dopant diffusion or thermal annealing for achieving excellent passivation and contacting properties. This extra process is eliminated in the fired passivating contact (FPC) approach used for simplified fabrication of poly-Si/SiO x passivating contacts. Instead, FPCs rely on the thermal budget of the fast/short and high-temperature firing process used for metallization of solar cells to achieve similar final properties. Despite this, compatibility of FPCs with industrially viable metallization techniques has not been demonstrated yet, which is studied in this work for fire-through Ag screen-printing and Ni/Ag plating. With screen-printing, low recombination current density (J 0) down to 4.9 fA/cm2, low contact resistivity between the Ag contacts and the FPC (ρ c,m) down to 7.2 mΩ⋅cm2, and Ohmic transport through the FPC including the SiO x film were achieved using wet-chemically grown SiO x. Nevertheless, J 0 of metallized regions (J 0,m) exceeded 1000 fA/cm2. Reducing J 0,m was attempted by mitigating the blistering observed in FPCs, but J 0,m remained high. With Ni/Ag plating, excellent surface passivation with J 0 down to 2.7 fA/cm2 and very low J 0,m < 50 fA/cm2 were achieved, but no Ohmic contacts could be obtained. Integration of screen-printed FPCs in large-area n-TOPCon solar cells was also demonstrated, yielding average efficiencies of 18.4%, limited mainly by the high J 0,m and series resistance of the FPCs. The results presented reveal the challenges for the industrialization of FPCs and provide valuable insights for tackling these. [Display omitted] • Fired passivating contacts (FPCs) developed relying only on the thermal budget of firing and not on conventional annealing. • Compatibility of FPCs with fire-through Ag screen-printing and Ni/Ag plating tested. • Screen-printing: J 0,pass ≈ 5 fA/cm2 & ρ c < 10 mΩ∙cm2 achieved, but J 0,metal was high. • Plating: J 0,pass < 3 fA/cm2 & J 0,metal < 50 fA/cm2 achieved, but contacts were non-Ohmic. • Integration of FPCs in screen-printed large-area n-TOPCon cells led to 18.4% efficiency. [ABSTRACT FROM AUTHOR]

This work evaluates the potential of selective epitaxy to mitigate the recombination losses at the p-type contact regions of plated bifacial n-type PERT cells. Following the growth of a 500 nm, 2.5 1019 cm−3 boron doped epitaxial layer at the emitter contact regions defined by laser ablation of the passivating dielectrics, both an increase in V oc (+6 mV) and FF (+1% absolute) are measured in the final cells compared to the reference with a homogeneous diffused emitter. These results come with an average efficiency gain of 0.3 and 0.5% absolute for front and rear side illumination, respectively. If the diffused, blanket emitter in the passivated regions is replaced by a thicker, lowly doped epitaxial profile (3 μm, 5 1018 cm−3) to further reduce recombination, an additional rise in implied V oc after metallization of 10 mV is estimated. This increase would be the result of a reduction in J 0,pass, emitter (down to 6 fA/cm2) and J 0,plated, emitter (down to 1967 fA/cm2). Image 1 • Selective growth of doped regions by epitaxy on laser ablated textured surfaces. • Metallization by simultaneous plating of n- and p-type contacts in bifacial cells. • Reduced J 0,plated for p-type contacts by doping profile engineering with epitaxy. • Thermal SiO 2 /PECVD SiN x passivation after epitaxy at the same level than ALD Al 2 O 3. • Gain in FF and V oc for bifacial cells with a selective epitaxial emitter approach. [ABSTRACT FROM AUTHOR]