We present a new process for the fabrication of high efficiency IBC solar cells with passivating poly-Si contacts for both polarities. Aiming at short processing times and keeping commercial adaption in mind, we use in-situ doped LPCVD (Low Pressure Chemical Vapor Deposition) poly-Si layers and perform all patterning steps with lasers. We show details on the process optimization for the laser structuring, that consists of the ablation of an SiO2 etch barrier followed by KOH etching of the exposed poly-Si layers. There is a large process window for the laser power for the layer stack we use in our experiment. This enables the removal of an n+-type doped poly-Si layer without damaging an underlying p+-type doped poly-Si layer. A batch with p-type Si cells using this new process results in a device with efficiency of 25.5 % on 3.97 cm2 large solar cells. We present an analysis of the light-IV parameters to disclose the dominating losses. With further optimization we demonstrate independently confirmed 26.0 % efficiency on 24.5 cm2 large solar cells from n-type Si.

Monolithic perovskite/silicon tandem photovoltaics are among the most promising high-efficiency technologies for next-generation photovoltaics. However, the commercial development of two-terminal (2T) tandem configurations is limited by their operational instability of wide-bandgap perovskite materials, which leads to current mismatch and increased sensitivity to solar spectral variations. Three-terminal (3T) tandem architectures offer a viable route to address these limitations. Here, we demonstrate the real-world advantages of 3T perovskite/silicon tandem solar cells in mitigating current mismatch limitations and losses arising from solar spectral variations. Our 3T tandem solar cells achieve a power conversion efficiency of 30.1%, integrating a front-side textured interdigitated back contact (IBC) and poly-Si on oxide contact (POLO) silicon bottom cell. This is one of the highest efficiencies reported for 3T tandem solar cells so far. Through a direct comparison of 2T and 3T tandem configurations enabled by a novel measurement framework, we reveal that 3T architectures decouple performance from perovskite bandgap constraints, alleviating the need for the current matching. Additionally, 3T tandem solar cells exhibit enhanced spectral resilience under varying solar spectra when the top cell limits the short-circuit current. These findings underscore the potential of 3T architectures for stable and efficient tandem photovoltaics under real-world operating conditions.

Integrating wide-bandgap organic-inorganic lead halide perovskite absorber layers with Si bottom solar cells into tandem architectures offers significant potential for increasing power conversion efficiency (PCE). However, achieving high-performance monolithic tandem devices remains challenging, particularly when processing perovskite top cells on top of industrial silicon bottom cells, featuring polycrystalline silicon on oxide (POLO) passivating contacts, as implemented in "TOPCon" solar cells. Here, we employ an advanced silicon bottom cell architecture incorporating full-area electron-selective POLO front contacts and laser-structured hole-selective POLO back contacts. We perform the N2 annealing at an elevated temperature of silicon bottom cells, effectively curing sputter-induced damage in the full-area electron-selective POLO contact of the recombination junction and enhancing the interface between transparent conductive oxide and the n-type doped poly-Si layer. Additionally, this annealing treatment likely improves the rear small-area contact between the aluminum (Al) and the p+ poly-Si. Furthermore, we investigate how the nickel oxide layer regulates the substrate morphology and affects the charge carrier mechanisms for the top perovskite solar cells. These strategies remarkably promote charge carrier management, achieving a monolithic perovskite/POLO-Si tandem solar cell with a PCE of 31%. Moreover, the unencapsulated tandem cell retained 93% of its initial efficiency after operating for 240 hours at maximum power point under one sun intensity, 25 degrees C, and 30% relative humidity (ISOS-L-1), the extrapolated T80 lifetime is estimated to be 740 hours.

Large surface area applications such as high-efficiency > 26% solar cells require surface patterning with 1-10 micrometers periodic patterns at high fidelity over 1-10 cm^2 areas (before up scaling to 1 m^2) to perform at, or exceed, the Lambertian (ray optics) limit of light trapping. Here we show a pathway to high-resolution sub-1 micrometer etch mask patterning by ablation using direct femtosecond laser writing performed at room conditions (without the need for a vacuum-based lithography approach). A Bessel beam was used to alleviate the required high surface tracking tolerance for ablation of 0.3-0.8 micrometer diameter holes in ~40 nm alumina Al2O3-mask at high writing speed, 7.5 cm/s; a patterning rate 1 cm^2 per 20 min. The plasma etching protocol was optimised for a zero-mesa formation of photonic crystal (PhC) trapping structures and smooth surfaces at the nanoscale level. Scaling up in area and throughput of the demonstrated approach is outlined.

The recent tremendous progress in monolithic perovskite-based double-junction solar cells is just the start of a new era of ultra-high-efficiency multi-junction photovoltaics. We report on triple-junction perovskite-perovskite-silicon solar cells with a record power conversion efficiency of 24.4%. Optimizing the light management of each perovskite sub-cell (∼1.84 and ∼1.52 eV for top and middle cells, respectively), we maximize the current generation up to 11.6 mA cm-2. Key to this achievement was our development of a high-performance middle perovskite sub-cell, employing a stable pure-α-phase high-quality formamidinium lead iodide perovskite thin film (free of wrinkles, cracks, and pinholes). This enables a high open-circuit voltage of 2.84 V in a triple junction. Non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency if stored in the dark at 85 °C for 1081 h.

In this contribution, we aim to progress towards a 3T perovskite/POLO²-IBC tandem cell with highest efficiency. For this purpose, we describe the design considerations for a 3T perovskite/POLO²-IBC tandem cell with respect to the choice of the top and bottom cell configurations and their interconnection. We identify pin perovskite solar cells (PSCs) with a band gap of around 1.6 eV spin-coated on a nano-textured p+/n+ poly-Si tunnel junction front side of a n-type unijunction POLO²-IBC bottom cells as a promising cell architecture. We report on the experimental progress with the pin PSCs on a nano-textured surface, POLO junctions optimized for textured and planar surfaces simultaneuously and the realization of the p+/n+ poly-Si tunnel junctions and ITO/n+ poly-Si recombination junctions. We fabricate high performance 3T POLO²-IBC bottom cells with p+/n+ poly-Si and with ITO/n+ poly-Si junctions on a nano-textured front side and find that the pseudo-J-V characteristics of both bottom cells is on par with our filtered single-junction 26.1%-efficient POLO²-IBC cells. Currently, we intergrate the pin PSC on the nano-textured bottom cell' font side and we will present 3T Pk/POLO²-IBC tandem cells at the conference.

The pursuit of ever-higher solar cell efficiencies has focused heavily on multijunction technologies. In tandem cells, subcells are typically either contacted via two terminals (2T) or four terminals (4T). Simulations show that the less-common three-terminal (3T) design may be comparable to 4T tandem cells in its compatibility with a range of materials, operating conditions, and methods for subcell integration, yet the 3T design circumvents shading losses of the 4T intermediate conductive layers. This study analyzes the performance of two superstrate 3T III-V-on-Si (III-V//Si) tandem cells: One has slightly greater current contribution from the Si bottom cell (GaInP//Si) and the other has substantially greater current contribution from the GaAs top cell (GaAs//Si). Our results show that both tandem cells exhibit the same efficiency (21.3%), thereby demonstrating that the third terminal allows for flexibility in the selection of the top cell material, similar to the 4T design.

Stability of the passivation quality of poly‐Si on oxide junctions against the conventional mainstream high‐temperature screen‐print firing processes is highly desirable and also expected since the poly‐Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J0) and interface state densities (Dit) of symmetrical samples with n‐type poly‐Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The Dit values are (3 ± 0.2) × 1011 and (8 ± 2) × 1011 eV/cm2 when fired at 620°C and 900°C, respectively. The activation energy in an Arrhenius fit of Dit versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from SiH bonds at the poly‐Si/SiOx interface is not the root cause of depassivation. Postfiring annealing at 425°C can improve the passivation again. Samples with SiNx capping layers show an increase in J0 up to about 100 fA/cm2 by firing, which can be attributed to blistering and is not reversed by annealing at 425°C. On the other hand, blistering does not occur in poly‐Si samples capped with AlOx layers or AlOx/SiNy stacks, and J0 values of 2–5 fA/cm2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J0 and Dit: thermal stress at the SiOz interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.

Three-terminal (3T) and four-terminal (4T) tandem photovoltaic (PV) devices using various materials have been increasingly reported in the literature, but measurement standards are lacking. Here, multiterminal devices measured as functions of two load variables are characterized unambiguously as functions of three device voltages or currents on hexagonal plots. We demonstrate these measurement techniques using two GaInP/GaAs tandem solar cells, with a middle contact between the two subcells, as example 3T devices with both series-connected and reverse-connected subcells. Coupling mechanisms between the subcells are quantified within the context of a simple equivalent optoelectronic circuit. Electrical and optical coupling mechanisms are most clearly revealed using coupled dark measurements. These measurements are sensitive enough to observe very small luminescent coupling from the bottom subcell to the top subcell in the prototype 3T device. Quick simplified measurement techniques are also discussed within the context of the complete characterization.

High-efficiency, four-terminal tandem solar cells composed of thin GaAs films mechanically stacked onto interdigitated back contact silicon solar cells with a glass interlayer are demonstrated. The optimal thickness of the absorber layer of a rear heterojunction GaAs subcell for use in four terminal tandem solar cells was studied. GaAs top cells with absorber layer thicknesses of 1.5, 1.9, 2.3, 2.8, and 3.5 μm were fabricated on glass and mechanically stacked onto interdigitated back-contact Si bottom cells. All tandem cells were found to have efficiencies above 30% under the AM1.5 G spectrum demonstrating a relatively weak sensitivity to thickness in the four-terminal configuration. We found the 2.8 μm absorber layer cell to have the highest top cell and tandem cell efficiency at 26.38% and 32.57%, respectively. Optical modeling with transfer matrix method for the planar top cell and Lambertian light trapping in the textured Si subcell, along with drift-diffusion Hovel equations, were used to show photon recycling enhancement to the effective diffusion length and VOC of the top cell as a result of the low-index glass interlayer.

We determined the density of defect states of poly-Si/SiOx/c-Si junctions featuring a wet chemical interfacial oxide from lifetime measurements using the MarcoPOLO model to calculate recombination and contact resistance in poly-Si/SiOx/c-Si-junctions. In samples that did not receive any hydrogen treatment, the Di(t),(cSi) is about 2 x 10(12) cm(-2) eV(-1) before firing and rises to 3-7 x 10(12) cm(-2) eV(-1) during firing at measured peak temperatures between 620 degrees C and 863 degrees C. To address the question of why Al0 x /SiN y stacks in contrast to pure SiN y layers for hydrogenation during firing provides better passivation quality, we have measured the hydrogen concentrations at the poly-Si/SiOx/c-Si interface as a function of AlOx layer thickness and compared these to J(0) and calculated si values. We observe an increase of the hydrogen concentration at the SiOx/c-Si interface upon firing as a function of the firing temperature that exceeds the defect concentrations at the interface several times. However, the AlOx layer thickness appears to cause an increase in hydrogen concentration at the SiOx/c-Si interface in these samples rather than exhibiting a hydrogen blocking property.

Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities − a POLO2-IBC cell − has to electrically isolate the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH's 26.1%-efficient POLO2-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p+-(i)-n+ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p+-(i)-n+ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO2-IBC cell. We attribute this to the formation of a conductive channel between the p+ and n+ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack.

The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by ∼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9 mA/cm2 absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to ∼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%.

By applying an interdigitated back contacted solar cell concept with poly-Si on oxide passivating contacts an efficiency of 26.1% was achieved recently. In this paper the impact of the implemented initially intrinsic poly-Si region between p-type poly-Si and n-type poly-Si regions is investigated. Two recombination paths are identified: The recombination at the interface between the initially intrinsic poly-Si and the wafer as well as the recombination across the resulting p(i)n diode on the rear side which is aimed to be reduced by introducing an initially intrinsic region. By using test structures, it is demonstrated that the width of the initially intrinsic region ((i) poly-Si region) has a strong influence on the recombination current through the p(i)n diode and that this initially intrinsic region needs to be about 30 μm wide to sufficiently reduce the recombination across the p(i)n diode. Lateral and depth-resolved time of flight secondary ion mass spectrometry analysis shows that the high-temperature annealing step causes a strong lateral inter-diffusion of donor and acceptor atoms into the initially intrinsic region. This diffusion has a positive impact on the passivation quality at the c-Si/SiOx/i poly-Si interface and is thus essential for achieving an independently confirmed efficiency of 26.1% with 30 μm-wide initially intrinsic poly-Si regions.

Tandem and multijunction solar cells offer the only demonstrated path to terrestrial 1-sun solar cell efficiency over 30%. Three-terminal tandem (3TT) solar cells can overcome some of the limitations of two-terminal and four-terminal tandem solar cell designs. However, the coupled nature of the cells adds a degree of complexity to the devices themselves and the ways that their performance can be measured and reported. While many different configurations of 3TT devices have been proposed, there is no standard taxonomy to discuss the device structure or loading topology. This Perspective proposes a taxonomy for 3TT solar cells to enable a common nomenclature for discussing these devices and their performance. It also provides a brief history of three-terminal devices in the literature and demonstrates that many different 3TT devices can work at efficiencies above 30% if properly designed.

Wide-bandgap the organo-metal halide perovskite solar cells (PSCs) are key for high performance perovskite-based tandem photovoltaics. One key aspect limiting the overall power conversion efficiency (PCE) in the 4-terminal tandem architecture is the imperfect transmission of the incident light below the bandgap of top PSCs. Here, we present periodic and disordered nanostructured ITO electrodes as new strategies to reduce reflection losses and transmission of PSCs. Using the nanostructured ITO, the short-circuit current-density is improved compared to planar references and as a result, an increase in the overall PCE of the solar cells is achieved.

Three-terminal tandem solar cell with conductive adhesive interconnect and back-contacted bottom cell delivers 27.3% efficiency.