Gallium-doped silicon material has been rapidly gaining importance in the photovoltaic industry as a boron-oxygen defect-free material with promising minority carrier lifetime. We investigate the ...influence of different cell process flows passivated emitter and rear cell tunneling-oxide-passivating contact, and a "hot oxidation" process on the bulk material quality of an industrial Ga-doped Cz-grown silicon material, as well as its light- and elevated temperature induced degradation degradation behavior under light at elevated temperature. We measure a generally high carrier lifetime level, which remains limited by an unknown recombination-active defect after most processes. Hydrogenation seems to passivate this unknown defect. In addition, we demonstrate that such high-quality p-type material can suffer noticeably by iron even for extremely low concentrations below 10 9 at/cm 3 .
The response of lifetime samples made from boron‐ and gallium‐doped Czochralski‐grown silicon from the same producer to light‐ and elevated temperature‐induced degradation (LeTID) conditions (varying ...illumination at 75 °C), to dark anneals (DAs) at 175 °C, and the temporary recovery (TR) reaction under different conditions is investigated. It is found that Ga‐doped samples behave very differently than their B‐doped counterparts: while the carrier lifetime remains at a high level if an illumination equivalent to 1 sun at 75 °C is applied, strong carrier lifetime degradation occurs at low light intensities. A capture cross‐sectional ratio in degraded Ga‐doped samples of ~26 is found, which is typical for the LeTID defect. TR of this degraded state is observed on Ga‐doped samples when the illumination intensity is increased at 75 °C and when samples are illuminated at 25 °C with intermediate intensity. During DA of B‐doped samples, a bulk‐related degradation and a subsequent surface‐related degradation are observed. In contrast, degradation of Ga‐doped samples during DA only occurs on long timescales, and its cause is not clear, yet. It is concluded that the specific dopant species plays an active role both during LeTID and for surface‐related degradation—possibly as a result of differences in the acceptor–hydrogen pair properties.
Light‐ and elevated temperature‐induced degradation and surface passivation degradation of Ga‐doped silicon substrates show a different dependency on temperature and illumination conditions compared with their B‐doped counterparts. This may be related to the different binding properties of the acceptor–hydrogen pairs. These results are crucial for ensuring the long‐term stability of current passivated emitter and rear contact solar modules.
Czochralski‐grown gallium‐doped silicon wafers are now a mainstream substrate for commercial passivated emitter and rear cell (PERC) devices and allow retention of established processes while ...offering enhanced cell stability. We have assessed the carrier lifetime potential of such Czochralski‐grown wafers in dependence of resistivity, finding effective lifetimes well into the millisecond region without any gettering or hydrogenation processing, thus demonstrating one advantage over boron‐doped silicon. Second, the stability of gallium‐doped PERC cells are monitored under illumination (>3000 h in some cases) and anomalous behavior is detected. While some cells are stable, others exhibit a degradation then recovery, reminiscent of light and elevated temperature‐induced degradation (LeTID) observed in other silicon materials. Surprisingly, cells from one ingot exhibit LeTID‐like behavior when annealed at 300 °C but near stability when not annealed, but, for another ingot, the opposite is observed. Moreover, a stabilization process typically used to mitigate boron–oxygen degradation does not influence any cells that are studied. Secondary‐ion mass spectrometry of the PERC cells reveals significant concentrations of unintentionally incorporated boron in some cases. Nevertheless, even in the absence of mitigating light‐induced degradation, Ga‐doped silicon is still more stable than unstabilized B‐doped silicon under illumination.
Gallium‐doped silicon wafers are now a mainstream substrate for commercial passivated emitter and rear cell (PERC) devices. Although more stable than boron‐doped silicon, Ga PERC cells exhibit anomalous light‐induced degradation and lifetime instability. The onset of degradation appears sensitive to cell processing and/or the Ga doped base silicon material. Correlations with gallium and unintentional boron doping are investigated.
In this work, the established method of iron imaging is transferred from B‐doped silicon to Ga‐doped material. For this purpose, the pairing and splitting conditions are investigated and a ...preparation procedure suggested that ensures a sufficient fraction of iron–gallium pairing and splitting, respectively. Furthermore the defect parameters available in literature are compared and evaluated for a suitable description of the injection dependent carrier lifetime measurements. A parameter set that enables a coherent and adequate iron evaluation is suggested. Thus, a robust method for spatially resolved determination of the interstitial iron concentration in Ga‐doped silicon wafers is presented.
In this work, the method of imaging interstitial iron concentrations is transferred to Ga‐doped silicon. A thorough evaluation of the SRH parameters for the FeGa defect from literature is performed and a choice of parameters suggested that enables a proper determination of interstitial iron. Thereby, a spatially resolved evaluation of the interstitial iron concentration is enabled.
Improving electrical and optical properties is important in manufacturing high‐efficiency solar cells. Previous studies focused on individual gettering and texturing methods to improve solar cell ...material quality and reduce reflection loss, respectively. This study presents a novel method called saw damage gettering with texturing that effectively combines both methods for multicrystalline silicon (mc‐Si) wafers manufactured using the diamond wire sawing (DWS) method. Although mc‐Si is not the Si material currently used in photovoltaic products, the applicability of this method using the mc‐Si wafers as it contains all grain orientations is demonstrated. It utilizes saw damage sites on the wafer surfaces for gettering metal impurities during annealing. Additionally, it can crystallize amorphous silicon on wafer surfaces generated during the sawing process to allow conventional acid‐based wet texturing. This texturing method and annealing for 10 min allow for the removal of metal impurities and effectively forms a textured DWS Si wafer. The results show that the open‐circuit voltage (ΔVoc = +29 mV), short‐circuit current density (ΔJsc = +2.5 mA cm−2), and efficiency (Δη = +2.1%) improved in the p‐type passivated emitter and rear cells (p‐PERC) manufactured using this novel method, as compared to those in the reference solar cells.
The novel method developed in this study, i.e., SDGT, combined both gettering and texturing methods to improve the Si wafer‐based solar cell production efficiency. The results show that the open‐circuit voltage (+29 mV), short‐circuit current density (+2.5 mA cm−2), efficiency (+2.1%) improved and reduction in Fe concentration compared with that of the reference solar cell.
The recombination parameter J 0 s provides an important metric to characterize surface recombination. For its calculation, numerous methods and models have to be applied. Since the models for the ...Auger and radiative recombination in crystalline silicon were recently revised, it is important to investigate the influence of these changes on J 0 s . The origin and possible ways of obtaining J 0 s from effective lifetime measurements as well as simulations are described in detail, including the potential to fit the full lifetime curve and a new approach that is based upon the reparameterization of the excess charge carrier density Δ n . Using the effective lifetime measurements, we find that J 0 s values determined with the older parameterization by Richter et al. will result in erroneous values up to 5 fA/cm 2 , depending on the chosen conditions. By simulating the recombination parameter J 0 s in near surface, highly doped structures, such as emitters, it is shown that these errors can even go up to 50%. If used in a simulation, we highlight the importance of having the parameterizations of surface recombination being determined with the corresponding parameterization of intrinsic recombination. Therefore, an update for the recombination at oxide-passivated and phosphorous doped surfaces is given that can be used with the new intrinsic recombination models. Finally, we give some best-practice examples on how recent improvements in effective lifetime measurements affect J 0 s values as well as possible pitfalls.
The recombination parameter J 0 s provides an important metric to characterize surface recombination. For its calculation, numerous methods and models have to be applied. Since the models for the ...Auger and radiative recombination in crystalline silicon were recently revised, it is important to investigate the influence of these changes on J 0 s . The origin and possible ways of obtaining J 0 s from effective lifetime measurements as well as simulations are described in detail, including the potential to fit the full lifetime curve and a new approach that is based upon the reparameterization of the excess charge carrier density Δ n . Using the effective lifetime measurements, we find that J 0 s values determined with the older parameterization by Richter et al. will result in erroneous values up to 5 fA/cm2, depending on the chosen conditions. By simulating the recombination parameter J 0 s in near surface, highly doped structures, such as emitters, it is shown that these errors can even go up to 50%. If used in a simulation, we highlight the importance of having the parameterizations of surface recombination being determined with the corresponding parameterization of intrinsic recombination. Therefore, an update for the recombination at oxide-passivated and phosphorous doped surfaces is given that can be used with the new intrinsic recombination models. Finally, we give some best-practice examples on how recent improvements in effective lifetime measurements affect J 0 s values as well as possible pitfalls.
Impact of a constant magnetic field on decomposition of supersaturated solid solution is investigated for the system Cu-Be-Ni. A technical bronze Cu-1.9Be-0.3Ni (in wt.%) was water-quenched after ...holding at 800°C (0.5 h) and subsequently heat treated at 325°C, 350°C and 400°C for 1 hour without and with application of a constant magnetic field of 0.7 T. The annealing in magnetic field is found to influence significantly the precipitation characteristics in diamagnetic Cu-based alloy, especially at 325°C. The nucleation barriers for discontinuous precipitation at grain boundaries are decreased, while the growth rates seem to be decreased, too, in magnetic field. A possible mechanism of the magnetic effect on discontinuous precipitation in the Cu-based is discussed.
PDF
