Optimisation of Intrinsic a-Si:H Passivation Layers in Crystalline-amorphous Silicon Heterojunction Solar Cells

Abstract Heterojunction silicon wafer solar cells using an intrinsic amorphous silicon (a-Si:H) thin-film passivation layer between the crystalline c-Si substrate and the thin-film emitter layer have proven to be a viable device structure for high efficiency. While microcrystalline μc-Si:H is a good candidate for the emitter layer due to its high doping efficiency, intrinsic a-Si:H with its low interfacial defect density, high optical bandgap and good passivation ability makes it the ideal buffer layer to passivate the crystalline silicon interface. In this study, we report the film properties of intrinsic a-Si:H passivation layers deposited using RF (13.56 MHz) PECVD, at different SiH4/H2 gas flow ratios, pressures and temperatures. Trends relating deposition conditions to relevant film characteristics, such as thickness, hydrogen bonding, optical bandgap, and effective carrier lifetime of the samples are discussed. Finally, symmetrical p+/i/c-Si wafer/i/p+ heterojunction lifetime test structures, using 20 nm thick p-doped μc-Si:H emitter layers and 10 nm thick intrinsic a-Si:H layers, were made using the optimised parameters for intrinsic a-Si:H layers (discussed in this paper) and for p-doped μc-Si:H layers (discussed in a companion paper [1] ). These yield an effective lifetime of 2.4 ms at an injection level of 1015 cm-3, and an implied Voc of 730 mV.

[1]  S. Shimizu,et al.  Key issues for fabrication of high quality amorphous and microcrystalline silicon solar cells , 2006 .

[2]  A. Aberle,et al.  Optimisation of p-doped μc-Si:H Emitter Layers in Crystalline-amorphous Silicon Heterojunction Solar Cells , 2012 .

[3]  B. Hoex,et al.  Silicon surface passivation by hot-wire CVD Si thin films studied by in situ surface spectroscopy , 2009 .

[4]  K. Yoon,et al.  Effect of hydrogen dilution on intrinsic a-Si:H layer between emitter and Si wafer in silicon heterojunction solar cell , 2008 .

[5]  M. Ivanda,et al.  Microstructural properties of dc magnetron sputtered a-Si:H by IR spectroscopy , 1992 .

[6]  J. Tauc,et al.  Optical properties and electronic structure of amorphous Ge and Si , 1968 .

[7]  W. V. Sark,et al.  Excellent crystalline silicon surface passivation by amorphous silicon irrespective of the technique used for chemical vapor deposition , 2011 .

[8]  Arvind Shah,et al.  From amorphous to microcrystalline silicon films prepared by / hydrogen dilution using the VHF 70 MHz GD technique , 1998 .

[9]  Markus Schubert,et al.  Low-temperature deposition of amorphous silicon solar cells , 2001 .

[10]  P. Yu,et al.  Effect of Hydrogen Dilution on the Intrinsic a-Si:H Film of the Heterojunction Silicon-Based Solar Cell , 2011 .

[11]  Effect of hydrogen passivation on polycrystalline silicon thin films , 2005 .

[12]  R. Schropp,et al.  Hydrogen at compact sites in hot-wire chemical vapour deposited polycrystalline silicon films , 2000 .

[13]  T. Mueller,et al.  High quality passivation for heterojunction solar cells by hydrogenated amorphous silicon suboxide films , 2008 .

[14]  Y. Andrault,et al.  Uniformity and Quality of Monocrystalline Silicon Passivation by Thin Intrinsic Amorphous Silicon in a New Generation Plasma-enhanced Chemical Vapor Deposition Reactor , 2010 .

[15]  Wmm Erwin Kessels,et al.  Ultralow surface recombination of c-Si substrates passivated by plasma-assisted atomic layer deposited Al2O3 , 2006 .

[16]  G. Beaucarne,et al.  Surface passivation properties of boron-doped plasma-enhanced chemical vapor deposited hydrogenated amorphous silicon films on p-type crystalline Si substrates , 2006 .

[17]  H. Diao,et al.  Structure, stability and photoelectronic properties of transition films from amorphous to microcrystalline silicon , 2005 .

[18]  H. Fujiwara,et al.  Real-time monitoring and process control in amorphous∕crystalline silicon heterojunction solar cells by spectroscopic ellipsometry and infrared spectroscopy , 2005 .

[19]  Claudia Felser,et al.  Powder magnetoresistance of Co2Cr0.6Fe0.4Al/ Al2O3 powder compacts , 2006 .

[20]  M. Kondo,et al.  Boron-doped a-Si:H∕c-Si interface passivation: Degradation mechanism , 2007 .

[21]  K. Kamisako,et al.  Hydrogenated amorphous silicon film as intrinsic passivation layer deposited at various temperatures using RF remote-PECVD technique , 2010 .

[22]  A. Shah,et al.  Passivation properties of amorphous and microcrystalline silicon layers deposited by VHF-GD for crystalline silicon solar cells , 1994 .

[23]  T. Mizutani,et al.  Structure of amorphous and microcrystalline silicon thin films prepared at various gas pressures and gas flow rates by hot-wire chemical vapor deposition , 2006 .

[24]  N. Duy,et al.  Hydrogenated Amorphous Silicon Layer Formation by Inductively Coupled Plasma Chemical Vapor Deposition and Its Application for Surface Passivation of p-Type Crystalline Silicon , 2009 .

[25]  M. Taguchi,et al.  Development status of high-efficiency HIT solar cells , 2011 .

[26]  Armin G. Aberle,et al.  Generalized analysis of quasi-steady-state and quasi-transient measurements of carrier lifetimes in semiconductors , 1999 .

[27]  B. G. Brooks,et al.  Optical characterization of amorphous silicon hydride films , 1980 .