Boron and oxygen contamination in Czochralski-grown (Cz) silicon leads to a degradation of the minority charge carrier lifetime within short times due to the formation of recombination active complexes. The formation of these complexes is investigated for longer times showing a further development of the defect. This development called 'regeneration' is triggered by illumination or applied forward voltages and leads to a new state of the defect. This new state of the defect is proven to be less recombination active allowing higher stable minority carrier lifetimes and conversion efficiencies of solar cells. The influences of temperature and light intensity are discussed.
A new reaction model concerning the boron-oxygen related degradation is presented, introducing a third recombination inactive state, that stabilizes the electrical parameters of Cz-Si solar cells, and the transition to this new inactive state is proven by experimental data. Furthermore, the stability under solar cell working conditions and the formation kinetics of this additional state are discussed.
Lock-in thermography (LIT) is a well-established tool for defect analysis of solar cells, but so far has been restricted to the measurement of metallized samples. The new light-modulated lock-in thermography (LimoLIT) described in this paper overcomes this restriction by generating the voltage modulation needed for detection from photovoltaic conversion of modulated light. Thus wafers can be measured during all stages of fabrication, a pn-junction provided. The contactless LimoLIT method shows a stronger measurement signal and invokes a current flow close to illuminated operating conditions of solar cells, whereas conventional LIT is only comparable to a dark I-V measurement.
A set of neighboring multicrystalline silicon wafers has been processed through different steps of solar cell manufacturing and then images were collected for characterization. The imaging techniques include band-to-band photoluminescence (PL), defect-band or subbandgap PL (subPL), and dark lock-in thermography (DLIT). Defect regions can be tracked from as-cut wafers throughout processing to the finished cells. The finished cell's defect regions detected by band-to-band PL imaging correlate well to diffusion length and quantum efficiency maps. The most detrimental defect regions, type A, also correlate well to reversebias breakdown areas as shown in DLIT images. These type A defect regions appear dark in band-to-band PL images, and have subPL emissions. The subPL of type A defects shows strong correlations to poor cell performance and high reverse breakdown at the starting wafer steps (as-cut and textured), but the subPL becomes relatively weak after antireflection coating (ARC) and on the finished cell. Type B defects are regions that have lower defect density but still show detrimental cell performance. After ARC, type B defects emit more intense subPL than type A regions; consequently, type B subPL also shows better correlation to cell performance at the starting wafer steps rather than at the ARC process step and in the finished cell.
The shortage of Si feedstock and the goal of reducing Wp costs in photovoltaics (PV) is the driving force to look for alternatives to ingot grown multicrystalline (mc) Si wafers which have the highest share in the PV market. Ribbon Si seems to be a very promising candidate as no kerf losses occur, resulting in reduced Si costs per Wp. In addition, there is no need for the energy consuming crystallization of the ingot and therefore energy payback times can be significantly reduced. The higher defect density in ribbon Si materials has to be taken into account during cell processing, but ribbon materials already commercially available show excellent efficiencies, while for the most promising techniques efficiencies are significantly lower, but very promising. In this presentation an overview of ribbon Si technologies currently under research will be given, based on available data on crystal growth as well as solar cell processing and cell parameters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.