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33rd European Photovoltaic Solar Energy Conference and Exhibition; 218-225, This paper discusses degradation phenomena in crystalline silicon. We present new investigations of the light- and elevated temperature induced degradation (LeTID) of multicrystalline silicon. The investigations provide insights into the defect parameters as well as the diffusivity and solubility of impurity species contributing to the defect. We discuss possible defect precursor species and can rule out several metallic impurities. We find that an involvement of hydrogen in the defect could explain the characteristic observations for LeTID. Furthermore, we demonstrate analogies to the light-induced degradation mechanisms at elevated temperatures observed in floatzone silicon, where several experimental results also indicate an involvement of hydrogen in the defect. Based on the similarities between multicrystalline and floatzone silicon we suggest that both degradation phenomena might be caused by the same or similar defects. As we do not expect large concentrations of cobalt in floatzone silicon, we suggest that complexes of intrinsic lattice defects and hydrogen might cause both degradation phenomena.

The photovoltaic industry has shown vigorous growth over the last decade and will continue on its trajectory to reach terawatt-level deployment by 2022–2023 and an estimated 4.5 TW by 2050. Presently, its elaboration is driven primarily by cost reduction. Growth will, however, be fuelled by the consumption of various resources, bringing with it unavoidable losses and environmental, economic, and societal impacts. Additionally, strong deployment growth will be trailed by waste growth, which needs to be managed, to support Sustainable Development and Circular Economy (CE). A rigorous approach to quantifying the resource efficiency, circularity and sustainability of complex PV life cycles, and exploring opportunities for partially sustaining industry growth through the recovery of high-quality secondary resources is needed. We create a high-detail digital twin of a Silicon PV life cycle using process simulation. The scalable, predictive simulation model accounts for the system's non-linearities by incorporating the physical and thermochemical principles that govern processes down to the unit operation level. Neural network-based surrogate functions are subsequently used to analyse the system's response to variations in end-of-life and kerf recycling in terms of primary resource and power consumption, PV power generation capacity, and CO2 emission. Applying the second law of thermodynamics, opportunities for improving the sustainability of unit operations, the larger processes they are the building blocks of, and the system as a whole are pinpointed, and the technical limits of circularity highlighted. We show the significant effects changes in technology can have on the conclusions drawn from such analyses.

We develop a method to quantify the local minority carrier diffusion lengths in interdigitated back-contact solar cells having a 10- µ m-thick liquid-phase crystallized (LPC) Si absorber by light-beam induced current (LBIC) measurements. The method is verified by 2-D simulations of the LBIC signals using ASPIN3. The effective minority carrier diffusion lengths determined this way range between 33 and 44 µ m inside a grain, which proves that advanced cell concepts like an interdigitated back contact (IBC) system are well suited for the LPC absorbers. Furthermore, the method has the potential to help improve the optimization of contact system geometries, and it may be used to understand the influences of different grain orientations and improve the LPC-Si absorber fabrication process.

Photovoltaic (PV)‐based solar hydrogen generation is a promising pathway for the scalable production of renewable fuels. Understanding the limitations of solar‐to‐hydrogen (STH) conversion efficiencies is critical to identify performance limits and conceptualize practical device designs. Herein, the losses in PV‐based solar hydrogen generation systems are quantified and the potential of loss‐mitigation techniques to improve the STH efficiency is assessed. The analysis shows that the two largest losses in an ideal system are current and voltage mismatches due to suboptimal system configurations and energy lost as heat in the PV component. A temperature‐dependent model is developed to evaluate the relative potential of two techniques to mitigate these losses: decoupling the PV system to remove current and voltage matching requirements and thermal integration to use the heat losses from PV to increase the electrolyte temperature and improve the reaction dynamics for water splitting. It is shown that optimal system configuration strategies provide more than three times the STH efficiency increase of thermal integration at high operating temperatures. Combining both techniques results in predicted STH efficiencies approaching 20% for low‐cost perovskite–silicon tandem‐based systems with earth‐abundant catalysts at realistic working temperatures.

Photovoltaic (PV) conversion of solar energy starts to give an appreciable contribution to power generation in many countries, with more than 90% of the global PV market relying on solar cells based on crystalline silicon (c-Si). The current efficiency record of c-Si solar cells is 26.7%, against an intrinsic limit of ~29%. Current research and production trends aim at increasing the efficiency, and reducing the cost, of industrial modules. In this paper, we review the main concepts and theoretical approaches that allow calculating the efficiency limits of c-Si solar cells as a function of silicon thickness. For a given material quality, the optimal thickness is determined by a trade-off between the competing needs of high optical absorption (requiring a thicker absorbing layer) and of efficient carrier collection (best achieved by a thin silicon layer). The efficiency limits can be calculated by solving the transport equations in the assumption of optimal (Lambertian) light trapping, which can be achieved by inserting proper photonic structures in the solar cell architecture. The effects of extrinsic (bulk and surface) recombinations on the conversion efficiency are discussed. We also show how the main conclusions and trends can be described using relatively simple analytic models. Prospects for overcoming the 29% limit by means of silicon/perovskite tandems are briefly discussed.

Float-zone silicon is often used as a supposedly stable high lifetime reference material. Here it is shown, however, that boron doped float-zone samples that underwent a fast firing step may suffer from a severe degradation in bulk lifetime during illumination at elevated temperatures. Furthermore, it is observed that silicon nitride related passivation may be affected by a long-term decrease in chemical passivation quality. A time and injection resolved visualization is introduced to quickly distinguish between these degradation features. Both bulk lifetime and chemical passivation quality are shown to recover at the same treatment conditions after longer treatment times.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 853-856, A new approach to model the impact of edge recombination within silicon solar cells using a 3D simulation of the entire cell geometry within Quokka3 is presented. The contribution of edge recombination within the space charge region (SCR), which is not directly accounted for in Quokka3’s skin concept, is included by an effective property, a localized edge-length specific saturation current density with an ideality factor of 2: J02,edge. A worst-case value of 19 nA/cm was found to be largely invariable for varying device properties. The new model is applied to predict the worst-case influence of the cut-edge within PERC half-cells. A moderate efficiency loss of 0.1 %abs is predicted, for which the SCR and non-SCR edge recombination contribute non-additive. Differentiating those two loss mechanisms reveals a very similar impact on light-JV characteristics dominantly on pseudo-fill-factor, whereas only the SCR mechanism is visible in dark-JV curves as an increased J02. This means that non-SCR edge loss contributions will be missed by the commonly applied dark-J02 characterization approach. Dedicated experiments to reveal the different mechanisms by measuring front and rear laser-scribed half-cell designs before cleavage are carried out and compared to the simulations results.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 348-352, The applicability of different high (low) work function thin films for the formation of alternative hole (electron) selective contacts is currently (re-) explored for silicon solar cells. To provide some insight into contact schemes based on induced junctions their operation principles, important design parameters and losses are reviewed experimentally and with the help of numerical device simulations. Simulations with Sentaurus TCAD are used to address the importance of the work function and an efficient tunneling transport. It is highlighted that “non-selective” contacts will not obey the standard diode theory. This calls for an adapted loss analysis and one approach for this is presented for different hole contacts prepared by evaporation, sputtering, atomic layer deposition and PECVD. The results show that the “classical” electrical losses of selective contacts, like recombination and ohmic transport which are well quantified by J0 and the ohmic contact resistance, are not sufficient for the evaluation of “non-selective” contacts.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 827-831, 10 μm thick liquid-phase crystallized silicon (Si) layers on 3.2 mm Borofloat 33 glass (5cm x 5cm) are fabricated by continuous wave line focus laser (808 nm). A sputtered SiO2/SiON layer stack has been implemented as barrier layer at the glass Si interface. Solar cells with interdigitated back contact are prepared on these multicrystalline layers by using low temperature ( 20 μm is found. Laserdoping and contacting using UV laser resulted in small (< 20 mV) loss of Voc(1sun). Crack formation in LPCSG absorbers after laser crystallization process presents technological problems in the preparation of the interdigitated metal contact.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 753-756, We describe a process sequence for bifacial heterojunction (HJT) solar cells with simultaneous plating on both sides from a developed copper electrolyte. The process comprises the deposition of a PVD seed layer, patterning by advanced inkjet printing of a hotmelt-ink mask and copper electroplating, followed by optional deposition of a capping layer such as immersion silver to facilitate interconnection in modules. Subsequently, the mask and the seed layer are chemically removed. Our copper electrolyte yields layers with very low internal stress when plating at high plating rates above 3 μm/min. The combination of a sputtered seed layer and electroplated copper with low internal stress allows for good adhesion even for very thick plated layers as required for instance for shingled solar cell interconnection or 6” IBC solar cells. An aperture conversion efficiency above 24% has been independently confirmed for a large area solar cell with a four busbar front grid utilizing an industrial heterojunction precursor.