• SHAOMIN LI

      Articles written in Bulletin of Materials Science

    • Study on the improvement of p-type multi-crystalline silicon material for solar cells by the hydrogenation with electron injection

      SHAOMIN LI JIANBO SHAO XI XI GUILIN LIU RUOYING PENG RULONG CHEN LIPING CHEN YANFENG JIANG XIAOFENG GU

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      In this paper, we have found that the efficiency of p-type mono-crystalline silicon (mono-Si) passivated emitter and rear contact (PERC) solar cells can be increased by 0.12%abs. with the process of hydrogenation with electron injection(HEI). However, the same scheme was not suitable for p-type multi-crystalline silicon (mc-Si) solar cells. To promote power conversion efficiency (PCE) for the mc-Si solar cells, we have explored a developed HEI process for the mc-Si solar cells to improve the device performance. Meanwhile, we also analysed the mechanization inside the solar cells after applying the HEI process. Through the design of experiment (DOE), the correlation among injection current, temperature, injection time and efficiency improvement was analysed in detail. It was proved that mc-Si solar cells require higher current injection andtemperature to passivate the complex impurities in the bulk, when compared to mono-Si solar cells.With the optimal scheme explored by this paper, the open circuit voltage (Uoc), short circuit current density (Jsc) and fill factor (FF) of p-type mc-Si solar cells, respectively, increased by 1.2 mV, 0.11 mA cm$^{−2}$ and 0.05% abs., respectively. The efficiency was improved about $0.11\pm 0.005$% abs.. These results will provide a certain method and basis for further improving the efficiency of mc-Si PERC cells and overcoming the light-elevated temperature-induced degradation by HEI process.

    • Impurity mechanism of monocrystalline silicon PERC solar cells stimulated by prelight-induced degradation

      JIANBO SHAO XI XI GUILIN LIU SHAOMIN LI RUOYING PENG GUOQING CHEN YONGFEI JIANG

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      Although the monocrystalline silicon (mono-Si)-passivated emitter and rear contact (PERC) solar cells have achieved incredible efficiency, they still can be further improved by hydrogenation. So the hydrogenation was performedto investigate the improvement of large area (>240 cm$^2$) mono-Si PERC solar cells and estimate the significance of previous light-induced degradation (pre-LID) under a high-intensity infrared (HI-IR) LEDs source platform. Then, theresults indicated that the parameters, such as open-circuit voltage ($U_{\rm oc}$) and short-circuit current density ($J_{\rm sc}$) and fill factor (FF), could be better improved after LED hydrogenation with the execution of the pre-LID. The efficiency of mono-Si PERC solar cells with pre-LID increased by $\sim$0.190 $\pm$ 0.005%$_{\rm abs.}$ for 2 min, which was higher than that without pre-LID (0.115 $±$ 0.005%$_{\rm abs.}$). Moreover, the results showed that the efficiency of large area mono-Si PERC solar cells with light-induceddegradation (LID) treatment after LED hydrogenation only existed a slight degradation of about $-$0.253 $\pm$ 0.005%$_{\rm rel.}$. Compared with mono-Si PERC solar cells without pre-LID, the efficiency improvement and LIDmitigation of mono-Si solar cells with pre-LID was faster and more significant by LED hydrogenation, so that the LED hydrogenation time significantly can shorten from 6 to 2 min. Additionally, the possible presence of a boron-oxygen (BO) model was estimated, and this BO model is susceptible to be activated by the injection of external energy, resulting in more BO defects in the process of pre-LID, so that subsequent hydrogenation rate becomes faster.

    • Photo-induced hydrogenation and rapid cooling measure on dislocation clusters of multi-crystalline silicon PERC solar cells

      JIANBO SHAO XI XI GUILIN LIU SHAOMIN LI RUOYING PENG GUOQING CHEN TUO ZHU

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      The dislocations are the deep level defects with a negative impact on the multi-crystalline silicon (mc-Si) solar cells. Though potential mechanisms of dislocation formation on the silicon ingot have been studied, few investigations consider the effect of LED hydrogenation on dislocation clusters. In this study, we have explored the influence of hydrogenation on the dislocation clusters of large-area ($244.34 \pm 0.05$ cm$^2$) mc-Si solar cells using the high-intensity infrared LED source. However, applying normal cooling measure to hydrogenation will trigger the instability of thehydrogenation improvement effect due to residual thermal stress, so we proposed an appropriate rapid cooling measure (RCM) followed by hydrogenation and achieved optimized results. The results indicated that electrical properties, minority carrier lifetime, current density, power density and external quantum efficiency were enhanced through LED hydrogenation and RCM, and the degradation of mc-Si solar cells also was significantly suppressed. To estimate the content of dislocations after LED hydrogenation and RCM, we applied the X-ray diffraction techniques to calculate the dislocation density using the full-width at half maximum of the rocking curve at (111), (220), (311), (400) and (331) reflections. The dislocation density of mc-Si PERC solar cells was decreased by $0.12 \times 10^8$ cm$^{-2}$ ($\pm 0.02 \times 10^8$ cm$^{-2}$) after LED hydrogenation and RCM. Meanwhile, photoluminescence images also illustrated that LED hydrogenation passivated dislocation clusters as well as impurities and defects gathered by dislocations. Therefore, LED hydrogenation of dislocation clusters is an effective measure to improve the performance of dislocation-containing mc-Si solar cells.

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      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
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      Posted on July 25, 2019

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