PL-based external radiative efficiency (ERE) and implied open-circuit voltage (iV OC) metrics were introduced for thin-film solar absorbers to better understand the voltage deficit and diagnose losses in solar cells. Traditionally, elevated ERE and iV OC measurements are associated with diminished recombination within the solar device, a rationale heavily reliant on the assumption of a uniform bandgap and high carrier mobilities in the absorber. In this study, we investigate the possible reasons of elevated iV OC in realistic CdSeTe absorbers with a graded Se profile. By employing light-induced transient grating measurements, we reveal that hole mobility significantly decreases—by more than an order of magnitude—with increasing Se content. Using detailed numerical models of iV OC, we examine how the bandgap nonuniformity and the reduced hole mobility within graded CdSeTe absorbers influence iV OC measurements. We show that high iV OC may result from inflated quasi-Fermi-level splitting in the front region of a CdSeTe absorber with slow hole transport. Based on our results, we conclude that the iV OC metric (or ERE metric) for graded CdSeTe devices may be misleading, is not suitable for quantitative assessments, and should not be used as a sole metric of absorber quality. We discuss possible ways to extract useful information from the iV OC–V OC gap by supplementing the front-side illumination measurements with back-side illumination measurements.

A new thermodynamic limit for the open circuit voltage of solar cells that includes thermalization is obtained in terms of photon entropy. A simple graphical construction makes it possible to link this limit to the existing limits for single junction cells due to Trivich and Flinn, Shockley and Queisser and Würfel, and the thermodynamic Carnot-type limit for hot-carrier solar cell. At the fundamental level, this limit points to similarity between photovoltaic and thermoelectric energy conversion.

not-yet-known not-yet-known not-yet-known unknown Silicon heterojunction technology (HJT) and tunnel oxide passivated contacts (TOPCon) solar cell technologies are expected to dominate the photovoltaic market in the coming years. However, there are still some concerns about the long-term stability of these technologies. This work examines the effects of two widely used commercial soldering fluxes (Flux A and Flux B) on the stability of commercial silicon HJT and TOPCon solar cells. The soldering flux was applied to the solar cells, and the solar cells were annealed at 85 oC under low relative humidity. TOPCon solar cells were found to be stable; however, significant degradation was observed in the HJT solar cells after only 50 hrs. The efficiency of the HJT cells decreased by ~ 61% rel with Flux A and ~ 55% rel with Flux B, respectively. We attribute part of the observed degradation to holes present in the HJT cell metalisation after printing, which allow the soldering flux to easily penetrate the contact and subsequently react with the paste constituents. In addition, we find that the indium tin oxide (ITO) layer is very sensitive to soldering flux, showing major cracks and significant peeling after 50 hrs of annealing. Consequently, this work shows that some soldering flux can react with the ITO layer, without requiring the presence of water. This suggests that certain types of soldering flux can harm HJT solar cells even after encapsulation without the need for moisture ingress. Therefore, paying more attention to the choice of soldering flux is essential, especially when working with HJT cells. It is strongly recommended that users perform comprehensive component analysis testing on soldering fluxes before their official use rather than solely relying on datasheets provided by suppliers.

A document by Aline Kirsten Vidal de Oliveira. Click on the document to view its contents.

We investigate rapid thermal processing (RTP) as alternative to the prolonged thermal annealing process used to form tunnel-oxide passivating contacts for silicon solar cells. The thermal treatment is generally followed by hydrogenation to passivate defects at the Si/SiOx interface. Whereas industrial manufacturing generally uses Cz wafers, research is often carried out with FZ wafers. Both types of wafers are prone to the formation of thermal defects in the bulk. To disentangle effects of the interface and the bulk, we assess the lifetime at different steps of the process sequence for both wafer types. We find that the initial bulk lifetime of our p-type FZ material is maintained for RTP up to temperatures of about 450°C, followed by a severe decay and eventually a moderate extent of recovery at temperatures above 800°C. Compared to FZ material, the initial bulk lifetimes in our p-type Cz material are slightly lower, but they are maintained on that level up to about 600°C. Beyond that temperature, the lifetimes also decay, but to a lesser extent than in the FZ material, and there is no curing at higher temperatures. Hydrogenation can partially passivate the bulk defects in FZ material, but the initial state is not recovered. In Cz material, it appears that RTP creates two different types of defects; for those created up to 800°C the initial state can be recovered by hydrogenation whereas those created at higher temperature cannot be passivated by hydrogenation. We also investigate the formation of n-type passivating contacts by RTP, and we fabricate solar cell precursors with a single RTP step and the same hydrogenation for both contact polarities. After sputtering a transparent conducting ITO layer on the full area and an Ag metallization, we achieve solar cells efficiencies up to 20.5%.

In this work, we demonstrate the formation of local boron doped, p+ SiO x/ poly-Si structures using wet chemical etching by direct printing of boron-ink FlexTrail printing. This process is a mask free approach for the formation of local TOPCon structures for high efficiency tunnel oxide passivated contact (TOPCon) solar cells. Factors affecting the etch back selectivity between intrinsic and boron doped poly-Si are studied. It is found that pre-treatment by diluted HF (1 wt%) before poly-Si removal by a KOH solution is the most crucial process to ensure etch selectivity. Etching the native oxide on intrinsic and keeping the boron silicate glass (BSG) layer on p+ poly-Si is the optimum condition for removing intrinsic poly-Si while having p+ TOPCon structure. Line widths in the range of of 86-100 µm and 24-40 µm were achieved on planar and textured surfaces, respectively. FlexTrail printing allows for significantly lower (and higher) feature sizes, but its fine-line potential wasn’t fully exploited here for alignment reasons of post-processing. Test structures with a line grid of local TOPCon structures featured a maximum open circuit voltage ( iV OC) value of 720 mV and lowest saturation current density of local p+ SiO x/ poly-Si (J 0SE) ~ 90-120 fA/cm 2. The developed local p+ poly-Si will be integrated in high efficiency TOPCon solar cell where p+ poly-Si will be placed under the metal contact in the very near future.

Due to their significantly lower costs than their compound semiconductor counterparts, there is increasing interest in using silicon solar cells for specific cost-sensitive applications in space, particularly in low Earth orbit (LEO). A major concern is, however, that the minority carrier lifetime (referred to henceforth as lifetime) of silicon solar cells experiences severe degradation in space due to the impact of irradiation by high-energy electrons and protons. Fortunately, thermal and hydrogenation processes can recover the lifetime losses caused by some (potentially all) defects. In this work, we study these radiation-induced defects and their recovery in detail using contactless lifetime measurement and deep-level transient spectroscopy (DLTS). Both fired and unfired industrial Ga-doped passivated emitter and rear contact (PERC) solar cell precursors are used in this work. The precursors were irradiated with 1 MeV electrons and annealed at 300 °C and 380 °C, respectively. All the irradiated samples exhibited lifetime recovery at both annealing temperatures, and the fired samples recovered significantly quicker and reached higher saturated lifetime values. After only ~360 s of annealing at 380 °C, the irradiated fired samples recovered to their pre-irradiation lifetime. In contrast, the irradiated non-fired samples required 71.5 times longer (25,740 s) at 380 °C to reach saturation. Remarkably, longer annealing times result in a reduction of the lifetime, which could be due to surface-related degradation. The DLTS measurements revealed a clear reduction of recombination active defects after annealing, including V-V + and C i-C s in irradiated fired samples and V-V + in irradiated unfired samples. This study demonstrates that the firing process is critical for optimizing the recovery of irradiation damage in silicon solar cells. Hydrogenation of the silicon bulk results in quicker recovery and superior End-of-life performance compared to thermal annealing without bulk hydrogen. Therefore, Ga PERC solar cells with bulk hydrogenation can recover radiation-induced damage, rendering it more suitable for missions in LEO.

We present an analysis of the performance data of a monitored PV system onboard a light commercial electric vehicle during parking and driving conditions. The PV system’s nominal power is 2180 WP with flat silicon modules on the vehicle’s roof, rear, left, and right sides, as well as other electronic components needed to charge the vehicle’s high-voltage (HV) battery. The analysis indicated that after 488.92 hours of operation, the modules mounted on the vehicle roof produced 133.32 kWh of electricity during parking compared to 15.4, 30.67, and 22.99 kWh for the modules mounted on the rear, left, and right sides, respectively. During the trips, after 31.99 hours of operation, 6.12, 0.68, 1.08, and 1.86 kWh of electricity were produced by the modules on the roof, rear, left, and right sides, respectively. The overall system efficiency was in the 60-65 % range. The aggregated usable electricity reaching the HV battery after multiple conversion stages generated by the system at the two parking locations was 129.39 kWh. PV electricity generated at the two parking locations enabled a range extension of approximately 530 km, which is 30% of the total distance driven during the measurement period between April and July 2021.

Perovskite solar cells (PSCs) have exhibited significant advancements over the last decade, positioning them as the most promising candidate for the next-generation photovoltaic technology. Recently, significant efforts have been focused on the scale-up of PSCs towards enabling their commercialization. In this study, we performed electrical simulations to elucidate the balance between electrical and geometric losses in PSMs and verified our model by fabricating opaque (PSMs) and semi-transparent wide-bandgap perovskite solar modules (ST-PSMs). We showed that a P2 width of 20-50 µm provides an optimized P2 contact resistance, resulting in high geometric fill factors (GFF) and fill factor (FF), simultaneously. PSMs with an aperture area of 4.2 cm 2, reaching a GFF of 98.4%, an FF of 81.5%, and a PCE of 17.78% were fabricated. To demonstrate the scalability of this approach, 16 cm 2 PSMs, reaching a GFF of 97.0%, an FF of 80.1%, and a PCE of 17.58% were fabricated. ST-PSMs (4 cm 2) with >92.5% GFF, 81.4% FF, and 15.68% PCE were fabricated. We believe that the proposed optoelectronic model, along with its validation through the fabrication, exhibiting exceptionally high GFFs and FFs, elucidates the optical-electrical trade-off in PSMs and thus offers valuable insights for the design of highly efficient PSMs.

For the automated analysis of I/V-characteristics of solar cells and modules, descriptive parameters are essential. In particular with the rise in machine-learning techniques and the related increase data volumes, there is a need for good, general purpose, descriptive parameters. The most commonly used descriptive parameters for I/V are the standard solar cells parameters, consisting of V oc , I sc , V mpp , and I mpp . Also other representations may be considered, such as one diode model parameters corresponding to a particular I/V. However, these representations are very coarse and cannot distinguish or represent many common (non-ideal) features of an I/V (e.g. an S-shape). In this work we propose an extended set of solar cell parameters, which are well defined, and easy to determine. We evaluate the effectiveness of the extended solar cell parameters by reconstructing the I/V from the extracted parameters. This allows one to “measure” information loss. We compare the accuracy of our parameters with other commonly used curve models for I/V, namely the one diode model, and the Karmalkar-Haneefa model. The models are applied to a large set of I/V (about 2.2 million curves), covering a wide range of technologies and conditions. We demonstrate our extended solar cell parameters consistently provide an accurate description of nearly all I/V in these datasets. Furthermore, we present our I/V analysis tool which we use to process these datasets. This tool is fast and capable of extracting the extended solar cell parameters, as well as parameters for the one diode model and the Karmalka-Haneefa model. Finally, we exemplary show how the extended solar cell parameters may be used to detect partial shading in outdoor data, by training a simple random-forest classifier based on extended solar cell parameters.

A world record conversion efficiency of 26.81% has been achieved recently by LONGi team on industry-grade silicon wafer (274 cm 2, M6 size). An unparalleled high fill factor ( FF) of up to 86.59% boosted the cell performance. The theoretical FF limit has been predicted to be 89.26%, while the practical FF is far below this limit for a prolonged interval due to the constraints of recombination ( i.e., SRH recombination) and series resistance. The ideality factor ( m) in the equivalent circuit of silicon solar cells is consistently ranging from 1 to 2 and rarely falls below 1, resulting in a relatively lower FF than 85%. Here, this work complements a systematic simulation study to demonstrate how to approach the FF limit in silicon solar cell fabrication. Firstly, a diode component with an ideality factor equal to 2/3 corresponding to Auger recombination is incorporated in the equivalent circuit for LONGi’ ultra-high FF solar cell; Secondly, an advanced equivalent circuit is put forward for comprehensive analysis of bulk recombination and surface recombination on the performance, in which specific ideality factors are directly correlated with various recombination mechanisms exhibiting explicit reverse saturation current density ( J 0); Finally, we evaluate precisely the route for approaching theoretical FF in practical solar cell fabrication based on electrical design parameters using the developed model.

Each solar cell is characterized at the end-of-line using current-voltage ( IV) measurements, except shingle cells, due to multiplied measurement efforts. Therefore, the respective host cell quality is adopted for all resulting shingles, which is sufficient for samples with laterally homogeneous quality. Yet, for heterogeneous defect distributions, this procedure leads to (i) loss of high quality shingles due to defects on neighboring host cell parts, (ii) increased mismatch losses due to inaccurate binning and (iii) lack of shingle-precise characterization. In spatially resolved host measurements, such as electroluminescence images, all shingles are visible along with their properties. Within a comprehensive experiment 840 hosts and their resulting shingles are measured. Thereafter, a deep learning model has been designed and optimized which processes host-images and determines IV parameters like efficiency or fill factor, IV curves and binning classes for each shingle cell. The efficiency can be determined with an error of 0 .06 % abs enabling a 13 % abs improvement in correct assignment of shingles to bin classes compared to industry standard. This results in lower mismatch losses and higher output power on module level as demonstrated within simulations. Also IV curves of defective and defect-free shingle cells can be derived with good agreement to actual shingle measurements.

This study focuses on electron-selective passivating contacts for crystalline silicon (c-Si) solar cells where an interlayer is used to provide a low contact resistivity between the c-Si substrate and the metal electrode. These electron contact interlayers are used in combination with other passivating interlayers (e.g., a-Si:H, TiO2, and Nb2O5) to improve surface passivation whilst still permitting contact resistivities suitable for high efficiency solar cells. We show that a wide variety of thermally evaporated materials, most of which have ionic character, enable an Ohmic contact between n-type c-Si and Al. From this pool of compounds, we observed that CsBr has especially promising behavior because of its excellent performance and thermal stability when combined with thin passivating layers. With different test structures, we were able to demonstrate low contact resistance using TiO2/CsBr, Nb2O5/CsBr and a-Si:H/CsBr stacks on n-type c-Si. The quality of the provided surface passivation depended on the stack but we achieved the best overall passivation stability with TiO2/CsBr. Finally, we were able to demonstrate an efficiency >20% on a laboratory-scale solar cell that implements the TiO2/CsBr/Al stack as full-area rear side electron selective contact.