In this study, we investigated progression of potential-induced degradation (PID) in photovoltaic modules fabricated from n-type-based crystalline-silicon cells with front p+ emitters. In PID tests in which a bias of −1000 V was applied to the modules, they started to degrade within 5 s and their degradation saturated within 60 s. This behavior suggested that the PID was caused by positive charge accumulation in the front passivation films. Performing PID tests with a bias of −1500 V revealed that the degradation rate strongly depended on the applied bias whereas the saturation value was independent of the applied bias. Regeneration tests on degraded modules previously subjected to PID tests for durations of 5 and 10 min were performed by applying a positive bias of +1000 V. All the degraded modules completely recovered their performance losses within 60 s regardless of the degradation test duration. On the basis of these results, we proposed that these positive charges originate from positively charged K centers formed by extracting electrons from neutral and negatively charged K centers. This model readily explains the observed degradation and regeneration behavior. To test our model, we determined the fixed positive charge densities (Qf) of a silicon nitride passivation film before and after PID, for which it was found that Qf showed similar saturation behavior. Additionally, the saturated Qf value was of the same order as K center density. These results support our model involving a charging process of K centers.

This study addresses progression of potential-induced degradation (PID) of photovoltaic modules using n-type single-crystalline silicon cells. In a PID test in which a voltage of −1000 V was applied to the cells, the modules started to degrade within 10 s and the degradation saturated within 120 s, suggesting that PID is caused by positive charge accumulation in the front passivation films. We propose that these positive charges originate from positively charged K centers formed by extracting electrons from the K centers, which explains the rapid degradation and its saturation behavior. We obtain simulated and experimental results supporting this hypothesis.

Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates. The EC starts from the edges of the a-Si films due to additional heating from flash lamp light. This is followed by lateral crystallization with a velocity on the order of m/s, leaving behind periodic microstructures in which regions containing several hundreds of nm-ordered grains and regions consisting of only 10-nm-sized fine grains alternatively appear. The formation of the dense grains can be understood as explosive solid-phase nucleation, whereas the several hundreds of nanometer-sized grains, stretched in the lateral direction, are probably formed through explosive liquid-phase epitaxy. This phenomenon will be applied to the high-throughput formation of thick poly-Si films for solar cells.

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Polycrystalline silicon (poly-Si) films as thick as 4.5 mm are prepared by flash lamp annealing (FLA) of amorphous silicon (a-Si) films without thermal damage onto glass substrates. The a-Si films are deposited by catalytic chemical vapor deposition (Cat-CVD) at 320 C. Since the hydrogen content in Cat-CVD a-Si films is as low as 3 at. %, they are easily converted to poly-Si without any dehydrogenation treatment. Chromium (Cr) films 60 nm thick are coated onto glass substrates to achieve high area uniformity of poly-Si formation. Secondary ion mass spectroscopy (SIMS) reveals that no diffused Cr atoms are detected inside poly-Si films and that crystallization is not the well-known metal-induced crystallization. Raman spectra from the poly-Si films show high crystallinity close to 1, and the photoluminescence (PL) spectrum demonstrates clear band-to-band transition, indicating the formation of device-quality poly-Si by FLA of Cat-CVD a-Si.

Accelerated tests were used to study potential‐induced degradation (PID) in photovoltaic (PV) modules fabricated from silicon heterojunction (SHJ) solar cells containing tungsten‐doped indium oxide (IWO) transparent conductive films on both sides of the cells and a rear‐side emitter. A negative bias of −1000 V was applied to a module with respect to the cover glass surface in a chamber maintained at 85°C, which significantly reduced the cell's short‐circuit current density (Jsc) within several days. Based on dark current density‐voltage and external quantum efficiency measurements, the reduction in the Jsc was attributed to optical losses rather than carrier recombination. X‐ray absorption fine structure spectroscopy showed the formation of metallic indium (In) in the IWO layers of a degraded cell, which suggests that the root cause of the optical loss was a darkening of the front IWO layers caused by the precipitation of metallic In. In extremely severe PID tests, the SHJ PV modules exhibited not only a further reduction in the Jsc but also a moderate reduction in the open‐circuit voltage (Voc). These Jsc and Voc reductions were probably caused by sodium being introduced into the base region of the cells. A comparison of the PID test results of the SHJ PV modules with those of other types of PV modules indicates that SHJ PV modules have a relatively high resistance to PID. As a module with an ionomer encapsulant exhibited little degradation, their high resistances to PID may be further improved by using encapsulants with high electrical resistances.

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We precisely investigate sodium (Na)-induced potential-induced degradation (PID) in n-type front-emitter (n-FE) crystalline silicon (c-Si) photovoltaic (PV) modules, in which open-circuit voltage (Voc) and fill factor deteriorate. Secondary ion mass spectrometry shows Na introduction into n-FE cells by a negative-bias PID stress and a reduction in Na density by positive-bias application. Scanning electron microscopy and energy dispersive X-ray analysis reveal the formation of Na-based protrusions on the cell surface. Silicon nitride (SiNx) disappears at the position of protrusions, which is the root cause for the serious and unrecoverable PID of n-FE c-Si PV modules.