Abstract
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 °C and stays above 50 °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.”
Highlights
T HE PHOTOVOLTAIC (PV) industry is dominated by crystalline silicon solar cells and modules, and of these, approximately 40% of worldwide production uses boron-doped Czochralski (Cz) grown substrates [1]
Due to the existence of many forms of carrier- or light-induced degradation, a less ambiguous terminology to refer to this degradation is BO degradation, or BO-related carrier-induced degradation (CID) (BO-CID) [7]
A three-state hydrogen-based model is used here to describe the BO defect complex system that is associated with CID in boron-doped Cz silicon, as has been used by various authors [44], [63]–[65]
Summary
T HE PHOTOVOLTAIC (PV) industry is dominated by crystalline silicon solar cells and modules, and of these, approximately 40% of worldwide production uses boron-doped Czochralski (Cz) grown substrates [1]. Defect formation was identified as a limiting factor for enabling high-speed processes on finished cells without the requirement to degrade samples prior [53] These contributions have led to the development of multiple widely used commercial tools [54], [55], enabling manufacture of stable commercial cells and modules using boron doped Cz substrates. This work considers a self-repairing module concept [62] and investigates the potential in the field when no (or partial) BO-CID mitigation process is performed prior to installation This is based on the same modeling principle, including the other defect reactions in three-state BO defect system (to be discussed ) as a best case scenario
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