Control Charts and Efficient Sampling Methodologies in the Field of Photovoltaics

Industries must have their process under control in order to become more performant. This is true in particular for the photovoltaic (PV) industry. A Statistical Process Control (SPC) study has been realised for the semi-industrial process at IMEC. In these circumstances control charts have been built and sampling schemes have been investigated. It has been found to be powerful to detect special causes of variation and will still be used in the future for early detection of out of control situations

Wet chemical treatment of boron doped emitters on n-type (100) c-Si prior to amorphous silicon passivation

10.1016/j.apsusc.2014.11.180APPLIED SURFACE SCIENCE328140-14

Performance and thermal stability of an a-Si:H/TiOx/Yb stack as an electron-selective contact in silicon heterojunction solar cells

Low contact resistivity (ρc) and low recombination current density at the metallized area (J0,metal) are the key parameters for an electron-selective contact in solar cells, and an i-a-Si:H/TiOx/low work function metal (ATOM) structure could satisfy these criteria. In this work, to achieve strong downward band bending, an Yb (Φ = 2.5–2.6 eV)/Ag stack is used. Moreover, the impact of (1) substrate topography (flat or textured), (2) TiOx thickness, and (3) Ti precursor (TTIP vs TDMAT) on the ATOM contact performance is investigated. The results show that the ATOM contact is relatively insensitive to the surface topography and to the Ti precursors (TTIP or TDMAT) used for the atomic layer deposition (ALD) of TiOx. However, the TiOx thickness has a significant impact on the ρc and marginally on the J0,metal of the ATOM contact. For all topography cases and Ti precursors, 1 nm thick TiOx results in the lowest ρc value, most likely due to EF,metal depinning. In the silicon heterojunction solar cell, this ATOM contact (i-a-Si:H/TiOx/Yb/Ag) yields a solar cell efficiency of 19.2% with a high VOC of 723 mV without the need of a doped n-a-Si:H layer. Concerning the thermal stability of these contacts, TEM images confirm that Yb does not diffuse into the i-a-Si:H layer after an annealing at 180 °C for 30 min thanks to the TiOx layer behaving as a diffusion barrier. 98% of the initial solar cell efficiency is preserved even after successive annealing treatments at 150 and 175 °C, which are values in the same temperature range used in the module lamination and the sintering of the printed Ag. These results in combination with the demonstrated efficiency underline that the ATOM contact is a promising route to realize high-efficiency solar cells.\u3cbr/\u3e\u3cbr/\u3eKeywords: electron-selective contact; low work function metal; MIS contact; passivating contact; Y

Passivating electron-selective contacts for silicon solar cells based on an a-Si:H/TiO\u3csub\u3ex\u3c/sub\u3e stack and a low work function metal

\u3cp\u3eIn this work, the ATOM (intrinsic a-Si:H/TiO\u3csub\u3ex\u3c/sub\u3e/low work function metal) structure is investigated to realize high-performance passivating electron-selective contacts for crystalline silicon solar cells. The absence of a highly doped Si region in this contact structure is meant to reduce the optoelectrical losses. We show that a low contact resistivity (ρ\u3csub\u3ec\u3c/sub\u3e) can be obtained by the combined effect of a low work function metal, such as calcium (Φ 2.9 eV), and Fermi-level depinning in the metal-insulator-semiconductor contact structure (where in our case TiO\u3csub\u3ex\u3c/sub\u3e acts as the insulator on the intrinsic a-Si:H passivating layer). TiO\u3csub\u3ex\u3c/sub\u3e grown by ALD is effective to achieve not only a low ρ\u3csub\u3ec\u3c/sub\u3e but also good passivation properties. As an electron contact in silicon heterojunction solar cells, inserting interfacial TiO\u3csub\u3ex\u3c/sub\u3e at the i-a-Si:H/Ca interface significantly enhances the solar cell conversion efficiency. Consequently, the champion solar cell with the ATOM contact achieves a V\u3csub\u3eOC\u3c/sub\u3e of 711 mV, FF of 72.9%, J\u3csub\u3eSC\u3c/sub\u3e of 35.1 mA/cm\u3csup\u3e2\u3c/sup\u3e, and an efficiency of 18.2%. The achievement of a high V\u3csub\u3eOC\u3c/sub\u3e and reasonable FF without the need for a highly doped Si layer serves as a valuable proof of concept for future developments on passivating electron-selective contacts using this structure.\u3c/p\u3