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The origins of an increase in the series resistance of PERC multicrystalline silicon solar cells due to postfiring thermal processes are investigated. This effect has been shown to be capable of reducing the fill factor of finished cells by up to 20%ABS, severely degrading their performance. It is observed that electric currents applied either during or after these thermal processes can greatly alter the series resistance, either causing RS to increase by more than an order of magnitude or suppressing the effect entirely. It is demonstrated that this behavior is in good agreement with the expected interactions of hydrogen with dopants and electric fields within silicon wafers. It is therefore speculated that at least part of the observed increase in resistance is due to the motion of hydrogen within the cell itself.

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This paper presents OPEN, an open-source software platform for integrated modelling, control and simulation of smart local energy systems. Electric power systems are undergoing a fundamental transition towards a significant proportion of generation and flexibility being provided by distributed energy resources. The concept of 'smart local energy systems' brings together related strategies for localised management of distributed energy resources, including active distribution networks, microgrids, energy communities, multi-energy hubs, peer-to-peer trading platforms and virtual power plants. OPEN provides an extensible platform for developing and testing new smart local energy system management applications, helping to bridge the gap between academic research and industry translation. OPEN combines features for managing smart local energy systems which are not provided together by existing energy management tools, including multi-phase distribution network power flow, energy market modelling, nonlinear energy storage modelling and receding horizon optimisation. The platform is implemented in Python with an object-oriented structure, providing modularity and allowing it to be easily integrated with thirdparty packages. Case studies are presented, demonstrating how OPEN can be used for a range of smart local energy system applications due to its support of multiple model fidelities for simulation and control. Highlights • Presents the Open Platform for Energy Networks (OPEN), github.com/EPGOxford/OPEN • Integrated modelling, control & simulation framework for smart local energy systems • The object-oriented approach offers modularity, code reuse & extensibility • Development has been motivated by four industry-academic demonstration projects • Case studies demonstrate how OPEN can be extended for new applications

The silicon photovoltaic industry is currently shifting towards lightly doped emitters. These have electrical properties that benefit solar cells, compared to the traditional heavily doped emitters. This move brings new challenges, as gettering efficiencies of impurities are lowered as the doping reduces. This is particularly problematic in multicrystalline silicon (mc-Si) since cell performance is typically boosted by the effective gettering of such impurities. In prior work, we proposed the novel gettering technique, saw damage gettering (SDG), which improved effective carrier lifetime of standard performance mc-Si red zone material. In this work, we expand the study of SDG to various types of industrially relevant mc-Si: upgraded metallurgical grade (UMG), high performance bottom red zone (HPRZ), and diamond sawn high performance (DHP). The optimal condition for SDG is found to be an annealing temperature of 850 8C. With this condition it was demonstrated that the effective carrier lifetime can be increased in all silicon types upon SDG. The largest increase was observed for HPRZ material by a factor of 10, and the largest final effective lifetime post SDG was that of UMG, with t eff ¼ 61.3 ms. SDG is a potentially viable gettering method to work in conjunction with lightly doped emitters in removing the impurities of mc-silicon feedstock and thus, improving the efficiency of the cells made therefrom.

A new technique is described by which ionic species can be rapidly transported into oxide films, and once there provide effective and stable field effect passivation to silicon surfaces. Field effect passivation in thermally grown oxide films has been achieved by embedding potassium ions using a combined drift and diffusion mechanism at high temperature. This process has been shown to be over 10 times faster than a pure diffusion process. The resulting passivation stable for periods exceeding 600 days, with lifetimes reaching 1.4 ms, equivalent to a surface recombination velocity (SRV) ≤ 5.7 cm/s, on 1 Ωcm, n-type, FZ-Si.

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