Materials Science in Semiconductor Processing, 2020
Passivation of n-type and p-type monocrystalline CZ Si wafers (both polished and textured) with s... more Passivation of n-type and p-type monocrystalline CZ Si wafers (both polished and textured) with silicon oxide layers prepared by thermal (TO), chemical (CO) and plasma (PO) techniques have been extensively investigated from the measurement of minority carrier lifetime (τ) by transient electrical photoresponse method, density of interface states (N SS) measurement by capacitancevoltage study and silicon oxidation states by X-ray photoelectron spectroscopy (XPS) study of the SiO 2 /Si interface. It has been observed that N SS and τ have an inverse relation but the dependence is not linear. The method (TO, CO or PO) of oxide layer development has been found to play a crucial role to control the passivation of the c-Si wafer surface. It has been observed that the thermally grown oxide layer (TO) is superior among three oxide layers for all the different c-Si surfaces. Very low density of interface states (<5 � 10 11) were found in both p-type and n-type polished wafer passivated with TO layer. Highest lifetimes of 170 μs for n-type polished wafer and 102.74 μs for p-type polished wafer were obtained with TO. The amount of sub oxide formed at the interface of both n-and p-type of wafers during different oxidation process, may have some correlation with N ss which in turn determines the passivation quality of the wafers. Improvement of implied V oc for both polished and textured wafers (n-type and p-type) was found using thermally grown oxide with respect to others.
Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over... more Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over the existing silicon waferbased aluminium back surface field (Al-BSF) solar cell. The lower efficiency of Al-BSF is caused by a few drawbacks e.g. higher rear surface recombination and weaker electric field at the rear surface. These technical shortcomings can be mitigated by incorporating field-effect passivation (FEP) layer viz. aluminium oxide (Al 2 O 3) at the rear surface with a capping layer of SiN X on it. Conventionally two new processing steps utilizing two expensive equipments, green laser (532 nm) for laser ablation of the FEP and SiN X capping layer stack at the rear surface and single side etcher for rear side polishing of wafer are used for manufacturing of PERC cells. In this paper, we have shown that instead of these two new expensive processing equipments we can use the IR laser (1024 nm) and RIE etcher, which are commonly available for Al-BSF manufacturing line, for the fabrication of PERC solar cells. Using p-type wafers of rather modest quality (minority carrier lifetime of ≥10 µs) we have demonstrated improvement of the efficiency from 18.71 to 19.62% and enhancements in V OC and J SC from 628 to 646 mV and 38.59 mA/cm 2 to 39.82 mA/cm 2 , respectively. A thorough root-cause analysis has been carried out to optimize the two new approaches within the existing Al-BSF line for the fabrication of PERC solar cell.
Materials Science in Semiconductor Processing, 2020
Passivation of n-type and p-type monocrystalline CZ Si wafers (both polished and textured) with s... more Passivation of n-type and p-type monocrystalline CZ Si wafers (both polished and textured) with silicon oxide layers prepared by thermal (TO), chemical (CO) and plasma (PO) techniques have been extensively investigated from the measurement of minority carrier lifetime (τ) by transient electrical photoresponse method, density of interface states (N SS) measurement by capacitancevoltage study and silicon oxidation states by X-ray photoelectron spectroscopy (XPS) study of the SiO 2 /Si interface. It has been observed that N SS and τ have an inverse relation but the dependence is not linear. The method (TO, CO or PO) of oxide layer development has been found to play a crucial role to control the passivation of the c-Si wafer surface. It has been observed that the thermally grown oxide layer (TO) is superior among three oxide layers for all the different c-Si surfaces. Very low density of interface states (<5 � 10 11) were found in both p-type and n-type polished wafer passivated with TO layer. Highest lifetimes of 170 μs for n-type polished wafer and 102.74 μs for p-type polished wafer were obtained with TO. The amount of sub oxide formed at the interface of both n-and p-type of wafers during different oxidation process, may have some correlation with N ss which in turn determines the passivation quality of the wafers. Improvement of implied V oc for both polished and textured wafers (n-type and p-type) was found using thermally grown oxide with respect to others.
Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over... more Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over the existing silicon waferbased aluminium back surface field (Al-BSF) solar cell. The lower efficiency of Al-BSF is caused by a few drawbacks e.g. higher rear surface recombination and weaker electric field at the rear surface. These technical shortcomings can be mitigated by incorporating field-effect passivation (FEP) layer viz. aluminium oxide (Al 2 O 3) at the rear surface with a capping layer of SiN X on it. Conventionally two new processing steps utilizing two expensive equipments, green laser (532 nm) for laser ablation of the FEP and SiN X capping layer stack at the rear surface and single side etcher for rear side polishing of wafer are used for manufacturing of PERC cells. In this paper, we have shown that instead of these two new expensive processing equipments we can use the IR laser (1024 nm) and RIE etcher, which are commonly available for Al-BSF manufacturing line, for the fabrication of PERC solar cells. Using p-type wafers of rather modest quality (minority carrier lifetime of ≥10 µs) we have demonstrated improvement of the efficiency from 18.71 to 19.62% and enhancements in V OC and J SC from 628 to 646 mV and 38.59 mA/cm 2 to 39.82 mA/cm 2 , respectively. A thorough root-cause analysis has been carried out to optimize the two new approaches within the existing Al-BSF line for the fabrication of PERC solar cell.
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