W.J. Soppe

Roll to roll fabrication process of thin film silicon solar cells on steel foil

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process chain are: 1) application of an insulating barrier layer which enables texturization of the rear contact with submicron structures for light trapping; 2) Si deposition with remote, linear PECVD; 3) series interconnection by laser scribing and printing after deposition of the layers (reducing the total number of process steps). The barrier layer is primarily an enabler for monolithic series interconnection of cells, but we show that we can also fabricate any arbitrary sub-micron structure in this layer by hot embossing to achieve optimum light trapping in the solar cells. For deposition of doped and intrinsic silicon layers we use novel remote and linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. First pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil plus textured barrier layer yielded efficiencies of about 3.7%.

Electron energy-loss spectroscopy of boron-doped layers in amorphous thin film silicon solar cells

Electron energy-loss spectroscopy (EELS) is used to study p-doped layers in n-i-p amorphous thin film Si solar cells grown on steel foil substrates. For a solar cell in which an intrinsic amorphous hydrogenated Si (a-Si-H) layer is sandwiched between 10-nm-thick n-doped and p-doped a-Si:H layers, we assess whether core-loss EELS can be used to quantify the B concentration. We compare the shape of the measured B K edge with real space ab initio multiple scattering calculations and show that it is possible to separate the weak B K edge peak from the much stronger Si L edge fine structure by using log-normal fitting functions. The measured B concentration is compared with values obtained from secondary ion mass spectrometry, as well as with EELS results obtained from test samples that contain ∼200-nm-thick a-Si:H layers co-doped with B and C. We also assess whether changes in volume plasmon energy can be related to the B concentration and/or to the density of the material and whether variations of the volume...

Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates.

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: 1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; 2) Si deposition with remote, linear PECVD; 3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sou rees, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil with textured barrier layer yielded efficiencies of about 3.7%.

Remote linear radio frequency PECVD deposited high quality a-Si:H(P) layers and their application in SI heterojunction structures

In this paper, we report on deposition and properties of high quality boron doped p-type amorphous Si (a-Si:H(p)) layers on n-type float zone Si(100) wafers by remote linear radio frequency plasma-enhanced CVD. The a-Si:H(p) layers show excellent surface passivation that is comparable to the one of a-Si:H intrinsic layers (a-Si:H(i)), and high stability of the passivation when stored in the dark . Additionally, the measured dark conductivity of deposited a-Si(p) is increased up to ≫7×10−6 S/cm by annealing. In a Si heterojunction cell structure, the a-Si:H(p) layer will be the emitter on an n-type base wafer. The effective lifetime of test structures of a-Si(p)/c-Si(n)/a-Si(n) has approached 1 ms, and a high pseudo fill factor and open circuit voltage have been obtained from a SunsVoc measurement. We conclude that these a-Si:H(p) layers are very promising for the application in high performance silicon heterojunction solar cells without using an intermediate a-Si:H(i) layer.

MW plasma enhanced CVD of intrinsic Si for thin film solar cells

The aim of the thin film silicon PV research program at ECN is the development of highthroughput production technology for high efficiency, microcrystalline and amorphous thin film silicon photovoltaics (PV) on flexible substrates. For this purpose, a roll-to-roll system has been designed and constructed, consisting of three deposition chambers for the continuous deposition of n-type, intrinsic and p-type Si layer. In this paper, we will present optical and electrical characterisation of device quality intrinsic Si layers, deposited with Microwave (MW) plasma enhanced chemical vapour deposition (PECVD), with a special focus on UV-reflection spectroscopy (UVRS). UVRS can be used to determine the crystallinity in very thin silicon layer and is interesting as a possible inline tool for layer quality assessment and crystallinity control.