Fine line printed and plated contacts on high ohmic emitters enabling 20% cell efficiency

Abstract

The contact performance of seed-layer printed, fired and plated (SFP) contacts were studied on solar cells with different emitter sheet resistivities. For the seed layer of the SFP-contacts a special metal ink called SISC (seed layer ink for the metallization of solar cells), developed and fabricated at Fraunhofer ISE to contact lowly doped emitters was used. The doping profile and the surface concentration of active phosphorus are determined by secondary ion mass spectroscopy (SIMS) and by electrochemical capacitance voltage (ECV) measurements. Large-area Cz-silicon solar cells 12.5 � 12.5 cm2 were fabricated with sheet resistivities between 40 ¿/sq. and 130 ¿/sq. The cells are metalized with SFP-contacts and conventional screen print contacts for comparison. High fill factors above 79% on solar cells with lowly doped emitters (sheet resistance of 130 ¿/sq.) could be achieved with SFP-contacts. In contrast, for screen-printed contacts using standard Ag paste the FFs for such lowly doped emitters are reduced to values around 55%. The difference in contact formation is explained by contact resistance measurements together with images from the metal semiconductor junction. Using the SISC ink solar cells with 45 ¿m wide contact structures were processed on a high efficiency cell structure with a passivated rear surface and a 110 ¿/sq. emitter a FF of 81% was achieved resulting in a cell efficiency of ¿=20.6%

Experimental and analytical study of saturation current density of laser-doped phosphorus emitters for silicon solar cells

“…While advanced metallization concepts have already proven able to form good ohmic contacts on doping concentration E10 20 at/cm 3 , this may be more difficult to achieve using conventional screen-printing [18]. Recently published laser-doped selective emitter cells results with screen-printed contacts are yet promising [2,19].…”

“…p-type Cz shiny-etched substrates with a thickness of 300 mm, a base resistivity of [14][15][16][17][18][19][20][21][22] O.cm and a surface of 5 Â 5 cm 2 were used here. The samples first underwent a POCl 3 furnace diffusion consisting in a deposit step of 15 min at a temperature of 830 1C, followed by a short drive-in step.…”

Fundamental studies on the front contact formation resulting in a 21% efficiency silicon solar cell with printed rear and front contacts

“…For the rear side, we compared three different structures, one using a standard Al-BSF and two with a stack system of plasma assisted atomic layer deposited (PA-ALD) Al2O3 and PECVD SiNx / SiOx. In contrast to previous studies, where we used a thick thermal oxide for the rear passivation [2,5], we combined a thin layer d = 10 nm of atomic layer deposited (PA-ALD) Al2O3 with a capping layer d = 90 nm of either SiNx or SiOx, depending on the used rear side metallization, screen printed Al-paste or evaporated Al.…”

“…The seed ink, developed at Fraunhofer ISE -which is called SISC (seed layer ink for the metallization of solar cells) -was already tested on emitters with a sheet resistivity up to RSH = 130 Ω/sq. [5] and successfully applied on a high efficiency solar cell where cell results up to η = 20.3% were achieved [2]. In this paper we present the fundamental investigations upon which the ink development is based.…”

Towards ink-jet printed fine line front side metallization of crystalline silicon solar cells

“…Moreover, by laser drilled opening and by modification of the screen printing process, maximum cell efficiency upto 16.1% are reached for mc-si metal wrap through solar cells (cell area: 125 Â 125 mm 2 and emitter sheet resistance: 65 O/sq) [6]. Recently, a two-layer process: aerosol printed fine line followed by light-induced plating (LIP) to contact solar cells with an emitter sheet resistance as high as 130 O/sq with the resulted solar cell efficiency of 20.6% has been reported [7].…”