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Modulation doping of silicon has great potential for miniaturization, surface passivation, and third generation photovoltaics (PV). At a modulation-doped silicon surface, we observe the formation of a 2D hole layer at the silicon surface at low temperatures by means of photoluminescence (PL) measurements. A line shape analysis of band–band and hot luminescence reveals the hole density (which is equal to the modulation-doped acceptor density). A high excitation intensity leads to a Fermi edge singularity of the band–band and hot PL emission. While the 2D layer can be characterized by the observed luminescence, the spectral region of twice the bandgap is fully dominated by emission from this surface layer, impeding the measurement of bulk hot luminescence, e.g., from Auger electrons or from nonthermalized carriers in a hot carrier PV device. [ABSTRACT FROM AUTHOR]

In recent years, significant attention has been paid to the research of light‐ and elevated‐temperature‐induced degradation (LeTID) in silicon solar cells due to the substantial power loss and instability it causes. It has been discovered that the presence of hydrogen is closely linked to the occurrence of LeTID. In this study, a thorough review and re‐assessment of previously published results is conducted and connected with newly obtained data. The findings indicate a complex interaction between different hydrogen complexes and the LeTID defect states. The precursor of LeTID is connected to molecular hydrogen (H2), while the LeTID degradation and regeneration are related to the binding of atomic hydrogen to the precursor and defect, respectively. A detailed description of the various reactions that occur under illumination and in the dark is provided. Additionally, explanation is given on how pre‐annealing can significantly affect the kinetics of LeTID during subsequent light soaking. Furthermore, a comprehensive hydrogen model that incorporates these various reactions and demonstrates an agreement between simulation and experimental results is developed. Finally, the implications of the findings on strategies for mitigating LeTID are discussed. [ABSTRACT FROM AUTHOR]

Optical losses of perovskite/silicon tandem solar cells can be effectively reduced by optimizing the thin‐film layer thicknesses. Herein, the thicknesses of DC sputtered indium tin oxide (ITO) films, which serve as the front electrode and the recombination layer connecting the subcells, are optimized to reach high transparency and good lateral charge transport simultaneously. Optical simulations of the full perovskite/silicon tandem solar cell stacks are performed to find the optimum recombination and front electrode ITO thicknesses for solar cells as well as modules. Implementation of the optimized 25 nm front electrode ITO thickness in semitransparent single‐junction perovskite solar cells increases the short‐circuit density by 1.5 mA cm−2 compared to the former reference thickness of 75 nm. Combined with an optimized 20 nm recombination ITO layer, high short‐circuit density of 20.3 mA cm−2 is reached in perovskite/silicon tandem solar cell devices, which is the highest reported value for planar front perovskite/silicon tandem solar cells to the best of knowledge. Further interface passivation enables 28.8% power conversion efficiency. [ABSTRACT FROM AUTHOR]

In the midterm future, the photovoltaic industry is expected to be dominated by two‐terminal (2T) perovskite–silicon (pero–Si) tandem solar cells, which have high energy conversion efficiency and require characterization for large‐scale production. Electroluminescence (EL) imaging is one of the most prevalent and nondestructive techniques for defect detection, recognition, and characterization in Si‐solar cells in mass production. This work presents an EL setup that enables fast, simultaneous, and separate luminescence capture from the two subcells of pero–Si tandem devices. To demonstrate the setup, several encapsulated 2T pero–Si tandem samples are investigated. First, the effect that resistive coupling between the two subcells has on defect appearance in EL images is recorded. Therefore, EL image under different operational conditions is recorded. A strong dependence of defect signatures on current injection is observed, that is explained partly by resistive coupling but partly as well by injection‐dependent changes of the prevalent defects in the cells. An investigation of preconditioning under dark forward operation reveals significant local decrease of EL intensity going along with rapid reversible or irreversible and severe degradation close to the edges of the samples. This degradation takes place under forward bias during a period of ≈1 h. [ABSTRACT FROM AUTHOR]

Perovskite‐based triple‐junction solar cells have recently gained significant attention and are rapidly developing, thanks to the insights gained from the advancement in its dual‐junction counterparts. However, employing perovskite materials in multijunction solar cells with more than two junctions brings new challenges that have not yet been addressed. One aspect is the possibility of reverse bias breakdown of perovskite subcells during operation of the triple–junction device. This is more relevant for triple‐junction solar cells because a higher reverse voltage might drop at perovskite subcells compared to the case of dual‐junction solar cells. Herein, the breakdown voltages of the two perovskite subcells in perovskite/perovskite/silicon triple‐junction solar cells are determined by progressively increasing the reverse bias applied to the subcells in a single‐junction architecture during current–voltage measurements and monitoring the appearance of shunts using illuminated lock‐in thermography measurements. Furthermore, to analyze the effect on the final triple–junction solar cell, the triple‐junction device is brought in different current limitation conditions. It is shown that the subcell breakdown can happen during the operation of the triple‐junction solar cell, especially for the case where the perovskite top cell is limiting the overall current of the device. This effect is less severe when the middle perovskite cell limits the current due to the absence of a direct contact with the silver metallization which has shown to be the major degradation site during reverse biasing of perovskite solar cells. Finally, there is no concern regarding breakdown of the silicon bottom cell due to the higher breakdown voltage of silicon compared to perovskite. [ABSTRACT FROM AUTHOR]

Solar simulators based on light-emitting diodes (LEDs) usually consist of many spectrally different LEDs, which in sum produce a sun-like spectrum. On the one hand, this results in the advantage of a high spectral tunability of these systems and on the other hand, however, also in the challenge of a high number of parameters which have to be set for the adjustment of a suitable simulator spectrum. Multijunction solar cells consisting of series-connected subcells are very sensitive to spectral irradiance conditions, which are affecting the current and the fill factor of the device. A precise adjustment of the simulator spectrum based on the spectral responsivity of the subcells is therefore essential for accurate multijunction measurements. Therefore, the number of spectrally different light sources used should be at least as high as the number of subcells in the device under test. However, for the measurement of multijunction devices, the much higher number of spectrally different light sources in common LED solar simulators results in a plethora of different simulator spectra, potentially suitable for the measurement. Furthermore, the nonlinear intensity characteristics of the utilized LEDs as well as the distance-dependent illumination uniformity of such solar simulators add complexity when aiming for a precise spectral adjustment. To tackle these challenges, a new spectral adjustment procedure which is based on a least square's solution algorithm and the definition of appropriate boundary conditions for the calculation of suitable simulator settings is introduced in this publication. Focusing on measurements carried out under constant illumination makes the presented method especially applicable for perovskite-on-silicon multijunction devices. Therefore, an adapted method for the determination of the solar simulator's spectral properties, considering thermal influences which are particularly relevant when carrying out continuous illumination measurements, is introduced in this work. The presented method is verified applying it on a Wavelabs SINUS 220 LED solar simulator by performing a measurement comparison on a multijunction solar cell with Fraunhofer ISE CalLab's well-established multilight source solar simulator. [ABSTRACT FROM AUTHOR]

In recent years, significant progress has been made in terms of efficiency and stability of perovskite on silicon (Pero/Si) tandem solar cells. Nevertheless, most of these activities are focused on small‐area laboratory cells while the availability of large‐area solar cells suitable for module integration on an industrial level remains limited, and therefore, measurements of tandem modules are rare. However, the reliable measurement of tandem modules is a prerequisite to evaluate the real potential of this rapidly developing technology for the photovoltaic market. In this study, we present the first published outdoor measurement of a full‐size bifacial Pero/Si tandem solar cell module. Our focus is on analyzing the spectral influences on the outdoor performance of the device through a qualitative assessment of the modules I–V parameter conducted over the course of a measurement day. Based on continuous monitoring of the ambient and module conditions, we provide consistent explanations for the complex interplay between the incident irradiance on both the front and backside of the module, as well as the module temperature. Based on our findings, we finally discuss how to appropriately account for the influence of bifaciality in the case of bifacial tandem modules, where the procedures used for bifacial single‐junction devices cannot be easily applied due to subcell limitation effects. Throughout the study, we present important insights into the real‐world characteristics of a bifacial Pero/Si tandem model, discuss and explain various influences on the modules performance, and therefore provide crucial information for an optimal cell design for bifacial Pero/Si tandem devices. [ABSTRACT FROM AUTHOR]

The Metal Wrap Through+ (HIP-MWT+) solar cell is based on the PERC concept but features two additional electrical contacts, namely the Schottky contact between p-type Si bulk and Ag n-contact and the metal-insulator-semiconductor (MIS) contact on the rear side of the cell below the n-contact pads. To prevent thermal hotspots under reverse bias, both contacts shall either restrict current flow or allow a homogenous current flow at low voltage. In this work we present both options. First the stable reverse bias characteristics up to −15 V with a MIS contact using industrially manufactured SiON passivation and second, an integrated by-pass diode using AlOX as insulator in the passivation stack allowing current flows at approximately Vrev = –3.5 V depending on the chosen screen-print paste. The examined Schottky contacts break down at around Vrev = –2.5 V. Reverse bias testing of the cells reveals a solid performance of the cells under reverse bias and an average conversion efficiency of η = 21.2% (AlOX) and η = 20.7% (SiON), respectively.

Spectrometric characterization allows for accurate determination of the current matching point and investigation of sub‐cell properties of multi‐junction solar cells. It is widely used for dual‐junction solar cells. Although the concept is suggested for triple‐junction solar cells, it is only applied for the variation of two sub‐cells. In this work, the applicability and evaluation procedure for a systematic variation of all three sub‐cells of a triple‐junction solar cell are presented. Clearly defined measurement conditions are derived which allow for meaningful characterization and comparisons of different triple‐junction devices. The presented procedure is exemplarily tested on a III–V on silicon triple‐junction solar cell using an light‐emitting diode‐based solar simulator where all needed spectral conditions can be calculated in advance and accordingly adjusted. Spectral conditions around the air mass 1.5 global spectrum are chosen and a fit routine to determine the current matching point from the discrete measurement points is proposed and validated by a measurement with a higher resolution around the current matching point. Finally, it is shown that the spectral conditions applied during the measurement also reflect outdoor conditions. This highlights the relevance of the presented procedure beyond the determination of the current‐matching conditions. [ABSTRACT FROM AUTHOR]

The top cell of a perovskite silicon tandem solar cell requires several material layers on each side of the perovskite absorber to efficiently extract electrons and holes, respectively. These layers must meet multiple requirements simultaneously, namely, low interface recombination, good charge carrier selectivity, low contact resistivity, and high optical transparency. Due to the complex architecture, characterization techniques are required in material and process optimization to identify loss mechanisms. Spatial resolution of the characterization is gaining importance along with the upscaling of the perovskite technology. Herein, electro‐ and photoluminescence (EL and PL) imaging is combined with illuminated lock‐in thermography (ILIT) for a comprehensive electro‐optical characterization of both subcells in perovskite silicon tandem devices with state‐of‐the‐art cell architecture. Thereby, the combination of the presented characterization methods together with numerical simulation models enables to carry out holistic investigations of device limitations. The strength of this approach is showcased by one particularly remarkable feature that is observed in the investigated tandem device, showing a low PL but high EL signal at local spots. Together with multidimensional optoelectrical device simulations, the measurements are explained and the root cause of this feature to originate from the perovskite/C60 interface is suggested. [ABSTRACT FROM AUTHOR]

Al2O3 is one of the most effective dielectric surface passivation layers for silicon solar cells, but recent studies indicate that there is still room for improvement. Instead of a single layer, multilayers of only a few nanometers thickness offer the possibility to tailor material properties on a nanometer scale. In this study, the effect of various plasma treatments performed at different stages during the ALD deposition of Al2O3/SiO2 multilayers on the silicon surface passivation quality is evaluated. Significant improvements in surface passivation quality for some plasma treatments are observed, particularly for single Al2O3/SiO2 bilayers treated with a H2 plasma after SiO2 deposition. This treatment resulted in a surface recombination parameter J0 as low as 0.35 fA cm−2 on (100) surfaces of 10 Ω cm n‐type silicon, more than a factor of 5 lower than that of Al2O3 single layers without plasma treatment. Capacitance‐voltage measurements indicate that the improved surface passivation of the plasma‐treated samples results from an enhanced chemical interface passivation rather than an improved field effect. In addition, a superior temperature stability of the surface passivation quality is found for various plasma‐treated multilayers. [ABSTRACT FROM AUTHOR]