The single-diode model (SDM) is the foundation of most photovoltaic yield simulations, but it becomes inaccurate for ultra-high-efficiency silicon devices where intrinsic recombination dominates. Here we present an “intrinsic-adjusted” extension to the single-diode model that explicitly accounts for intrinsic recombination. We compare this intrinsic-adjusted model to standard single-diode models using both simulated and experimental I-V data. We also investigate the use of additional fitting parameters, such as the device width and internal and external series resistances.The intrinsic-adjusted models reduced root-mean-square error by up to an order of magnitude for the simulated data and by a factor of three for the measured data, with improved accuracy near the maximum power point and open-circuit voltage. These results highlight the necessity of incorporating intrinsic recombination into modelling next-generation solar cells and suggest a pathway to more reliable yield simulations as commercial silicon photovoltaic technology approaches its intrinsic efficiency limits.

ABSTRACT This study investigated the thermomechanical stress induced by annealing plated Cu contacts on pyramidal surfaces of Si heterojunction (SHJ) solar cells. The homogeneity of cell temperature during annealing was assessed by both experiment and simulation. Several influential factors on the Si stress were evaluated, including Cu geometries, contact edge locations, contact width, pyramid size, and annealing temperature. The simulated stress, which was verified by Raman spectroscopy, was applied to predict the probability of fracture in combination with the Weibull diagram obtained from four‐point flexural (4PF) tests. Despite the identification of limiting flaw populations at the Si surface of Cu‐plated SHJ cells, a low fracture probability was estimated for a typical annealing temperature of 200°C.

To unlock the full performance potential of silicon heterojunction solar cells requires reductions of parasitic absorption and shadowing losses. Yet the translation of the hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) window layer and copper-plated electrodes to a cost-effective and scalable production-relevant context remains one of the largest roadblocks towards mainstream adoption of silicon heterojunction technology. Here we address the first challenge by developing an industrial-scale high-frequency plasma-enhanced chemical vapour deposition system with a minimized standing wave effect, enabling the deposition of doped nc-SiOx:H with excellent electron selectivity, low parasitic absorption and high uniformity. Next, we demonstrate seed-free copper plating, resulting in grids with a high aspect ratio and low metal fraction. By implementing the doped nc-SiOx:H window layer, certified efficiencies of 25.98% and 26.41% are obtained for M6-size bifacial silicon heterojunction devices with screen-printed silver electrodes and copper-plated electrodes, respectively. These results underline the performance potential of silicon heterojunction technology and lower the threshold towards their mass manufacturing. By tuning the plasma frequency, Yu, Gao et al. develop an industrial-scale chemical vapour deposition system for uniform nanocrystalline silicon oxide coatings, enabling 26.41% efficiency in silicon heterojunction solar cells with copper electrodes.

The first reports of both boron–oxygen (BO)‐related light‐induced degradation (BO‐LID) and amorphous/crystalline silicon heterojunction (SHJ) solar cell fabrication date back to the early 1970s. However, the complete development of the “modern” SHJ structure took place well before BO defect stabilization processes were developed. Due to the susceptibility of p‐type Czochralski (Cz)‐grown silicon to BO‐LID, such wafers were deemed unsuitable for SHJ solar cells. In addition to stability issues, lower charge carrier lifetimes due to contamination and challenges with surface passivation posed barriers to the adoption of p‐type wafers in SHJ applications. Herein, these three key challenges are discussed in detail. Kinetic modeling and experimental results reveal the severe impact of BO‐LID in p‐type SHJ solar cells and provide possible explanations as to why earlier attempts using p‐type wafers might have failed. The role of gettering and advanced hydrogenation in stabilizing BO defects in SHJ solar cells is demonstrated experimentally. Finally, a summary of the effective surface recombination velocities reported in the literature for hydrogenated intrinsic amorphous silicon passivation of p‐ and n‐type crystalline silicon wafers is presented. Based on these findings, the potential of p‐type wafers to enable a next‐generation of high‐efficiency solar cells featuring carrier‐selective contacts is discussed.

Copper (Cu) is present not only in the electrode for inverted-structure halide perovskite solar cells (PSCs) but also in transport layers such as copper iodide (CuI), copper thiocyanate (CuSCN), and copper phthalocyanine (CuPc) alternatives to spiro-OMeTAD due to their improved thermal stability. While Cu or Cu-incorporated materials have been effectively utilized in halide perovskites, there is a lack of thorough investigation on the direct reaction between Cu and a perovskite under thermal stress. In this study, we investigated the thermal reaction between Cu and a perovskite as well as the degradation mechanism by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Kelvin probe force microscopy (KPFM). The results show that high temperatures of 100 °C induce Cu to be incorporated into the perovskite lattice by forming "Cu-rich yet organic A-site-poor" perovskites, (CuxA1-x)PbX3, near the grain boundaries, which result in device performance degradation.

In this article, we study the kinetics of firing-activated degradation and recovery of industrially processed n+-doped poly-Si on thin oxide passivation layers subjected to illuminated annealing at elevated temperatures. The impact of a comprehensive range of fast-firing conditions on the subsequent degradation and recovery were assessed. The results indicate that the recovery process is dependent on the peak firing temperature, where higher temperatures led to an improvement in effective lifetime of up to 20% compared to the pre-fired state, and a very low surface dark saturation current density of 2.9 fA/cm2. By cycling through light soaking and dark anneal conditions, we show that unlike the commonly studied boron-oxygen light-induced degradation (BO-LID) and light- and elevated temperature-induced degradation (LeTID), this newly observed instability in n+-doped poly-Si passivation layers is not reversible, that is, once a degradation/recovery cycle is completed, the lifetime remains very stable under subsequent light soaking. This indicates that the surface related instability may be able to be completely resolved following the completion of the first degradation/recovery cycle. With this in mind, we investigate the potential for high intensity laser illumination (up to 150 kW/m2) to rapidly increase the recovery rates, however, this does not seem sufficient to cycle through degradation and recovery on a timescale that is amenable with mass production. The mitigation of any potential instabilities at the poly-Si interface has significant implications for the reliability of n-type tunneling oxide passivated contact (TOPCon) solar cells.

Surface‐related degradation (SRD) is a phenomenon whereby recombination in the near‐surface region of silicon wafers increases under elevated temperatures with or without carrier injection. Because of its importance for solar cell processing and operation, SRD occurring under light soaking at temperatures between 80 and 200 °C has recently attracted great interest. In this work, two post‐firing processes that can affect the formation of SRD are investigated. The first is the replacement of the passivating dielectric layers and the second is the use of thermal annealing between 300 and 400 °C. Post‐firing etching and redeposition of dielectric layers have minimal impact on subsequent degradation. In contrast, a thermal anneal at 400 °C for 30 min can reduce the extent of SRD by a factor of 6. These results imply that the interface between silicon and the dielectric itself is not the critical factor in the formation of SRD. The most likely explanation is that thermal processing causes an alteration in the silicon substrate that affects the subsequent formation of SRD.

The wide variety of silicon materials used by various groups to investigate LeTID make it difficult to directly compare the defect concentrations (N t) using the typical normalised defect density (NDD) metric. Here, we propose a new formulation for a relative defect concentration (β) as a correction for NDD that allows flexibility to perform lifetime analysis at arbitrary injection levels (Δn), away from the required ratio between Δn and the background doping density (N dop) for NDD of Δn/N dop = 0.1. As such, β allows for a meaningful comparison of the maximum degradation extent between different samples in different studies and also gives a more accurate representative value to estimate the defect concentration. It also allows an extraction at the cross-over point in the undesirable presence of iron or flexibility to reduce the impact of modulation in surface passivation. Although the accurate determination of β at a given Δn requires knowledge of the capture cross-section ratio (k), the injection-independent property of the β formulation allows a self-consistent determination of k. Experimental verification is also demonstrated for boron-oxygen related defects and LeTID defects, yielding k-values of 10.6 ± 3.2 and 30.7 ± 4.0, respectively, which are within the ranges reported in the literature. With this, when extracting the defect density at different Δn ranging between 1014 cm−3 to 1015 cm−3 with N dop = 9.1 × 1015 cm−3, the error is less than 12% using β, allowing for a greatly improved understanding of the defect concentration in a material.

Illuminated solar cells are susceptible to various degradation mechanisms that can act to reduce the total energy yield when deployed. One potentially severe form is an increase in carrier recombination in the surface regions. This effect has been reported at both the undoped rear surface and phosphorous diffused emitter of PERC solar cells. This work investigates the influence of a range of surface conditions on the surface-related degradation (SRD) behaviour in PERC solar cells. It is shown that SRD is strongly affected by the doping profile of phosphorous emitters, the use of thin thermal oxides with SiNx:H dielectric passivation layers, the substrate material, and the configuration of the rear surface passivation. It finds that more lightly doped emitters result in more front side SRD, with its extent increasing with the introduction of the SiO2/SiNx:H surface passivation layers. Czochralski silicon (Cz-Si) wafers were observed to be significantly more susceptible to surface degradation than multi-crystalline silicon (mc-Si) wafers, which we attribute to less trapping of hydrogen in the bulk of those substrates. On the rear side of PERC cells, surface degradation was only observed in structures that incorporated the combination of SiO2/SiNx:H rear layers. No SRD was observed in the existing Al2O3/SiNx:H technology used in the industrial PERC cells studied. However, the results presented have implications for future commercial solar cell technologies, which are transitioning towards lightly doped emitters and commonly incorporate thermal oxides for surface passivation.

Tunnelling oxide passivated contact (TOPCon) solar cells are gaining significant commercial interest, due to the potential for high efficiency. Industrially, this passivated contact scheme is typically coupled with an n-type Czochralski (Cz) wafer. JinkoSolar Holding Co., Ltd. is one of the leading manufacturers that are producing n-type TOPCon solar cells (referred to as 'HOT' cells) on a commercial scale. In this work, the influence of a post-cell hydrogenation step, using illumination from an LED light source, on the performance and stability of n-type TOPCon solar cells is investigated. The incorporation of this additional hydrogenation treatment led to an average efficiency enhancement of 0.64%(abs) on a batch of 50 cells made in an industrial environment. This significant improvement was caused by a 6.9 mV and 1.04%(abs) increase in open-circuit voltage (V-OC) and fill factor (FF), respectively. We also assessed the stability and found almost no light- and elevated temperature-induced degradation (LeTID) in hydrogenated n-type TOPCon cells. Testing at 70 +/- 5 degrees C under 1-sun illumination revealed that the maximum degradation is limited to 0.06%(rel). Following further stability testing, the efficiency increased beyond the initial value, up to 0.4%(rel) increase after 120 h. By incorporating this hydrogenation process into the production, an average line efficiency of 24.08% and V-OC of 707.5 mV was achieved. The champion cell from the batch displayed an efficiency of 24.58%, as certified by measurement at the Chinese Academy of Sciences.

At present, the commercially dominant and rapidly expanding PV-device technology is based on the passivated emitter and rear cell (PERC) design developed at UNSW. However, this technology has been found to suffer from a carrier-induced degradation commonly referred to as 'light- and elevated temperature-induced degradation' (LeTID) and can result in up to 16% relative performance losses. LeTID was recently shown to occur in almost every type of silicon wafer, independent of the doping material. Even though the degradation mechanism is known to recover under normal operation conditions, it is a lengthy process that drastically affects the energy yield, stability and, ultimately, the levelized cost of electricity (LCOE) of installed systems. Despite the joint effort of many research groups, the root cause of the degradation is still unknown. Here, we provide an overview of the existing literature and describe key LeTID characteristics and how these have led to the development of various theories of the underlying mechanism. Further, given the continuously appearing and strong evidence of hydrogen involvement in LeTID, many mitigation methods concerning hydrogenation have been suggested. We discuss such reported methods, bearing in mind crucial consumer necessities in terms of sustained cell performance and minimised LCOE.

Chapter Contents: 6.1 Hydrogen complexes with other species 6.1.1 Carbon-hydrogen (CH) complexes in silicon 6.1.2 Oxygen-hydrogen (OH) complexes in silicon 6.1.3 Carbon-oxygen-hydrogen (COH) complexes in silicon 6.1.4 Transition metal-hydrogen complexes in silicon 6.1.5 Vacancy-hydrogen complexes in silicon 6.2 Light- and elevated temperature-induced degradation 6.2.1 The impact of LeTID – cells, modules and systems 6.2.2 The key behaviours of LeTID 6.2.2.1 Dependence on firing on degradation extent 6.2.2.2 A universal defect in silicon 6.2.2.3 LeTID dependence on dielectrics 6.2.2.4 LeTID characterisation 6.2.3 The search for the root cause of LeTID 6.2.3.1 Metallic impurities 6.2.3.2 Hydrogen: a growing consensus 6.2.4 The role of hydrogen in LeTID 6.2.4.1 The impact of hydrogenated dielectric films 6.2.4.2 Direct correlation between hydrogen and LeTID 6.2.4.3 Analysis using DLTS 6.2.5 LeTID mitigation 6.2.6 Models for LeTID 6.2.7 LeTID in p-type silicon heterojunction solar cells 6.3 Negative effects due to hydrogen behaviour 6.3.1 Hydrogen-induced contact resistance 6.3.2 Neutralisation of charge and dopants 6.3.3 Formation of hydrogen-induced platelets 6.4 Summary Acknowledgement References

Light‐ and elevated temperature‐induced degradation (LeTID) can have significant and long‐lasting effects on silicon photovoltaic modules. Its behaviour is complex, showing highly variable degradation under different conditions or due to minor changes in device fabrication. Here, we show the large difference in LeTID kinetics and extents in multi‐crystalline passivated emitter and rear cell (multi‐PERC) modules from four different manufacturers. Varied accelerated testing conditions are found to impact the maximum extent of degradation in different ways for different manufacturers complicating the ability to develop a universal predictive model for field degradation. Relative changes in the open‐circuit voltage (VOC) have previously been used to assess extents of LeTID; however, due to the greater impact of the defect at lower injection, the VOC is shown to degrade less than half as much as the voltage at maximum power point (VMPP). The MPP current (IMPP) and fill factor (FF) also degrade significantly, having an even larger overall impact on the power output. These observations imply that currently employed methodologies for testing LeTID are inadequate, which limits the reliability of future predictive models. In light of this, the field must develop a more holistic approach to analysing LeTID‐impacted modules, which incorporates information about changes under MPP conditions. This will allow for a much clearer understanding of LeTID in the field, which will assist the performance of future PV systems.

In this work, the efficiency potential of the fully screen-printed passivated emitter and rear contact (PERC) solar cell structure is investigated via numerical simulations. A series of improvements and optimizations are performed on bulk quality, emitter properties and metallization of screen-printed PERC solar cells based on experimental results obtained in both industry and laboratory environments. With significantly improved bulk and surface passivation quality, we find that carrier recombination losses at the metal/silicon interface will impose a substantial limitation on efficiencies, highlighting the need for developing new screen-printing technologies to overcome the limitation from contact recombination. By improving the effectiveness of the back-surface field, reducing coverage area of laser-doped selective emitters and the front metal/silicon interface contact area, a 15 mV improvement in open-circuit voltage ( V OC ) was achieved in our modelled cells, due to greatly reduced contact recombination losses. With the further implementation of a multi-busbar and fine-line printing technologies, efficiency above 24% was obtained from simulations. Subsequently, a comprehensive pathway towards 24% efficiency for screen-printed PERC solar cells is proposed, without the need to implement passivated contacts or transition to a plated metallisation scheme. Key target requirements for future developments are also identified.

Halide perovskite‐based photovoltaic (PV) devices have recently emerged for low energy consumption electronic devices such as Internet of Things (IoT). In this work, an effective strategy to form a hole‐selective layer using phenethylammonium iodide (PEAI) salt is presented that demonstrates unprecedently high open‐circuit voltage of 0.9 V with 18 µW cm −2 under 200 lux (cool white light‐emitting diodes). An appropriate post‐deposited amount of PEAI (2 mg) strongly interacts with the perovskite surface forming a conformal coating of PEAI on the perovskite film surface, which improves the crystallinity and absorption of the film. Here, Kelvin probe force microscopy results indicate the diminished potential difference across the grain boundaries and grain interiors after the PEAI deposition, constructing an electrically and chemically homogeneous surface. Also, the surface becomes more p‐type with a downshift of a valence band maximum, confirmed by ultraviolet photoelectron spectroscopy measurement, facilitating the transport of holes to the hole transport layer (HTL). The hole‐selective layer‐deposited devices exhibit reduced hysteresis in light current density–voltage curves and maintain steadily high fill factor across the different light intensities (200–1000 lux). This work highlights the importance of the HTL/perovskite interface that prepares the indoor halide perovskite PV devices for powering IoT device.

The production and performance of p‐type inversion layer (IL) Si solar cells, manufactured with an ion‐injection technique that produces a highly charged dielectric nanolayer, are investigated. It is demonstrated that the field‐induced electron layer underneath the dielectric can reach a dark sheet resistance of 0.95 kΩ sq−1 on a 1 Ω cm n‐type substrate, lower than any previously reported. In addition, it is shown that the implied open‐circuit voltage of a p‐type IL cell precursor with a highly charged dielectric is equivalent to that of a cell with a phosphorous emitter. In the cell precursor, light‐beam‐induced current measurements are performed, and the uniformity and performance of the IL is demonstrated. Finally, simulations are used to explain the physical characteristics of the interface leading to extremely low sheet resistances, and to assess the efficiency potential of IL cells. IL cells are predicted to reach an efficiency of 24.5%, and 24.8% on 5/10 Ω cm substrates, by replacing the phosphorous emitter with a simpler manufacturing process. This requires a charge density of beyond 2 × 1013 cm−2, as is demonstrated here. Moreover, IL cells perform even better at higher charge densities and when negative charge is optimized at the rear dielectric.

Photovoltaic (PV) cells manufactured using p-type Czochralski wafers can degrade significantly in the field due to boron-oxygen (BO) defects. Commercial hydrogenation processes can now passivate such defects; however, this passivation can be destabilized under certain conditions. Module operating temperatures are rarely considered in defect studies, and yet are critical to understanding the degradation and passivation destabilization that may occur in the field. Here we show that the module operating temperatures are highly dependent on location and mounting, and the impact this has on BO defects in the field. The System Advisor Model is fed with typical meteorological year data from four locations around the world (Hamburg, Sydney, Tucson, and Wuhan) to predict module operating temperatures. We investigate three PV system mounting types: building integrated (BIPV), rack-mounted rooftop, and rack mounted on flat ground for a centralized system. BO defect reactions are then simulated, using a three-state model based on experimental values published in the literature and the predicted module operating temperatures. The simulation shows that the BIPV module in Tucson reaches 94 degrees C and stays above 50 degrees C for over 1600 h per year. These conditions could destabilize over one-third of passivated BO defects, resulting in a 0.4% absolute efficiency loss for the modules in this work. This absolute efficiency loss could be double for higher efficiency solar cell structures, and modules. On the other hand, passivation of BO defects can occur in the field if hydrogen is present and the module is under the right environmental conditions. It is therefore important to consider the specific installation location and type (or predicted operating temperatures) to determine the best way to treat BO defects. Modules that experience such extreme sustained conditions should be manufactured to ensure incorporation of hydrogen to enable passivation of BO defects in the field, thereby enabling a "self-repairing module."

Silicon heterojunction solar cells have historically had high open-circuit voltages due to the passivation provided by the intrinsic amorphous silicon layer, yet this same layer can also limit the fill factor of these devices. In comparison, diffused-junction solar cells have traditionally had higher fill factors than silicon heterojunction solar cells due to the low contact resistivity between the metal and doped surface of the wafer. By combining these two device architectures, it is possible to increase the fill factor-through a reduction in contact resistivity-while also maintaining a high open-circuit voltage with the passivating contact. In particular, we show through simulation and experiment that adding a diffusion under an amorphous silicon heterojunction contact reduces contact resistivity by approximately 0.04 Ωcm 2 , and, in contrast to standard silicon heterojunction devices, the contact resistivity does not increase with the intrinsic amorphous silicon thickness. In addition, this contact allows for an efficiency boost of 0.56-0.85% absolute over our standard device structure.

Herein, large‐area defect‐engineered p‐type silicon heterojunction (SHJ) solar cells using standard 1.6 Ω cm commercial‐grade boron‐doped Czochralski (Cz) silicon wafers are fabricated. It is demonstrated that despite achieving an open‐circuit voltage of 735 mV with an efficiency of 21.6% for gettered samples, without appropriate treatment, the cells are heavily susceptible to boron–oxygen‐related light‐induced degradation (LID), with the effective lifetime at maximum power point decreasing to 13 μs. This degradation results in a loss of efficiency of more than 3.1%abs (14.3%rel) after 48 h of light soaking. However, the addition of an advanced hydrogenation postcell fabrication process increases the efficiency by 0.2%abs to 21.8%, and dramatically reduces susceptibility of LID, decreasing the extent of degradation to 0.2%abs (0.9%rel). A peak stable independently measured efficiency of 22.0% with an open‐circuit voltage (VOC) of 736 mV is achieved with the addition of a dedicated high‐temperature prefabrication hydrogenation. These results indicate that p‐type Cz wafers can be used to fabricate stable, next‐generation high‐efficiency solar cells using silicon heterojunctions or other passivated contact architectures requiring VOCS well above 700 mV.