23% efficient p-type crystalline silicon solar cells with hole-selective passivating contacts based on physical vapor deposition of doped silicon films

Abstract

Of all the materials available to create carrier-selective passivating contacts for silicon solar cells, those based on thin films of doped silicon have permitted to achieve the highest levels of performance. The commonly used chemical vapour deposition methods use pyrophoric or toxic gases like silane, phosphine and diborane. In this letter, we propose a safer and simpler approach based on physical vapour deposition (PVD) of both the silicon and the dopant. An in-situ doped polycrystalline silicon film is formed, upon annealing, onto an ultrathin SiO x interlayer, thus providing selective conduction and surface passivation simultaneously. These properties are demonstrated here for the case of hole-selective passivating contacts, which present recombination current densities lower than 20 fA/cm 2 and contact resistivities below 50 mX cm 2. To further demonstrate the PVD approach, these contacts have been implemented in complete p-type silicon solar cells, together with a front phosphorus diffusion, achieving an open-circuit voltage of 701 mV and a conversion efficiency of 23.0%. These results show that PVD by sputtering is an attractive and reliable technology for fabricating high performance silicon solar cells.

Highly passivating and blister-free hole selective poly-silicon based contact for large area crystalline silicon solar cells

“…By fabricating similar samples using better quality KOH-polished 156psq n-type Cz c-Si wafers, an average iVoc of 731 mV was obtained after annealing at Ta = 700°C with a best value of 734 mV (corresponding to a J0 of 7 fA•cm -2 ). This is among the best values obtained so far with p + -poly-Si symmetrical samples on planar surface (in the range 732-735 mV for iVoc and 1-10 fA•cm -2 for J0) [14,20,21,23]. Values of 720 mV and 10 fA•cm -2 were also demonstrated on textured surface [22].…”

“…The SiOx layer growth (thermal or chemical) is followed by the deposition of a-Si or poly-Si layers either by Low-Pressure Chemical Vapor Deposition (LPCVD) [5][6][7], or by Plasma-Enhanced CVD (PECVD) [8][9][10][11][12][13]. Recently, the fabrication of poly-Si layers using Physical Vapor Deposition (PVD) was also demonstrated [14]. A consequent annealing step is performed to crystallize the deposited layer and/or activate dopants.…”

P‐Type Silicon Solar Cells with Passivating Rear Contact Formed by LPCVD p+ Polysilicon and Screen Printed Ag Metallization

“…After saw damage removal and wet‐chemical cleaning, the wafers are loaded in the quartz tube, in which they are subject to formation of a tunnel oxide by low temperature thermal oxidation and deposition of a 240 nm thick boron doped polysilicon layer by means of LPCVD. In a second tube, this layer is thermally annealed at 900°C for 30 min in N 2 ambient for dopant activation and contact improvement . Finally, a SiN x :H layer is formed on the rear side by PECVD in a direct plasma process.…”

“…Often, this material consists of a stack of a thin interfacial oxide layer, in combination with a highly doped silicon layer. Many technologies have been investigated for doped or undoped layer deposition, such as chemical vapor deposition, either plasma enhanced (PECVD), or under low pressure (LPCVD) or under atmospheric pressure (APCVD), recently also by physical vapor deposition (PVD) …”

“…Another paper showed a bifacial screen‐printed n‐type cell with a boron doped polysilicon rear emitter . Other work gave insight into high/low junction p‐type passivating rear contacts, in combination with a metallization by PVD, such as direct metal or a stack of a transparent conductive oxide and a metal . So far, limited literature data is available on p‐type passivating contact solar cells with screen printed metallization.…”