• GUILIN LIU

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

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

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

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.

• Infrared photon-assisted annealing for crystal engineering in perovskite solar cells

In this study, it was found that infrared-assisted annealing (IAA) was a novel and rapid method for growing of high-qualitied MAPbI$_3$ films. Compared to traditional thermal annealing, this new strategy combined high-intensity infrared photon flux into annealing process, which achieved the high-qualitied MAPbI$_3$ film with large crystalline grains and less surface defects. The reaction between MAI and PbI2 was characterized by confocal laser scanning and X-ray diffraction, which showed the addition of the infrared photons accelerated the reaction of the crystal, and the growth process of perovskite films with the increase of photon number is revealed. The simulation results revealed that infrared photons reduced the critical-free energy of crystallization of MAI and PbI$_2$, leading to the rapid growth of grains. Fabricated perovskite devices based on MAPbI$_3$ film obtained by this strategy produced optimized power conversion efficiency over 17% under only 5 min of IAA treatment, which increased by 2.6% compared to the thermal annealing. The efficiency improvement mainly attributed to better crystallinity, larger crystal grains under the IAA treatment, which had provided a new strategy for the future industrial production of perovskites.

• Accelerated potential-induced degradation technology for crystalline silicon cells

Potential-induced degradation (PID) is recently recognized as one of the most important degradation mechanisms in crystalline silicon cells as well as in photovoltaic (PV) modules. The ability of solar cells to resist PID effect is one of the key indicators of product quality monitoring. Traditional PID testing methods are complex and require up to 96 h in treating. To accelerate the PID test, a rapid PID treatment technology was urgent for PV field, which can extremely decrease the time expense. Hence, we have introduced a novel rapid PID treating technology, which reduced the treatment time from nearly 100 h to less than 8 h. This technology was applying an electric field directly on the solar cells to simulate the PID process of the modules. The process was named as electric field treatment (EFT). The effect of the applied EFT voltage on the solar cells was investigated from 1 to 1.8 KV. The degradation rate of the solar cells increased with increase in EFT voltage. The result of the energy dispersive spectrometer showed that the sodium element was found in the shunt area of the cell. It indicated that the microscopic principle of the power loss of the cell caused by the EFT was in accordance with that of the traditional PID. The electric performances of the cells treated by EFT showed that the PID test time can be accelerated to less than 8 h.

• # Bulletin of Materials Science

Volume 46, 2023
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020