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AI203 rear-passivated large-area silicon solar cells with screen-printed metallization are demonstrated for the first time.An industrially feasible solar cell process is described that is based on printing steps to contact base and emitter of large area solar cells with dielectric rear side passivation. The base of the cell is contacted at the rear by a full area screen-printed aluminum layer on an inkjet-structured AI20a/SiNx-layer stack. The AI rear contacts are co-fired with the screen-printed silver front contacts. The firing temperature is reduced to limit deterioration of the passivation ability of the aluminum oxide layer. Synergies are exploited by combining the structuring steps for the formation of openings in the rear side dielectric by hydrofluoric acid with the selective emitter formation on the front side.Investigations on lifetime samples show a 2.5-fold increase in effective lifetime for surfaces passivated by an AI20a/SiNx stack compared to fully metalized AI-BSF rear sides. This low surface recombination velocity is combined with a low contact resistance.On 125 x 125 mm2 boron-doped Czochralski wafers with resistivity of 3 Ocm an efficiency of 18.6% is achieved, that is a gain of 0.7% absolute compared to the efficiency of 17.9% of the best reference cells with a full area AI-BSF. An increase in the infrared spectrum of the internal quantum efficiency is determined as the source of this gain. Also, a higher reflectance at the rear side is measured that originates most probably from the Si/AI203 interface.The quality of the rear side passivation is assessed for the metalized and non-metalized area qualitatively and quantitatively. The local rear contacts are examined via scanning electron microscopy (SE M). A contact passivation mechanism based on a local BSF formation is found that is dependent on firing conditions.

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In this work, the back surface field (BSF) formation of locally alloyed Al‐paste contacts employed in recent industrial passivated emitter and rear cell solar cell designs is discussed. A predictive model for resulting local BSF thickness and doping profile is proposed that is based on the time‐dependent Si distribution in the molten Al paste during the firing step. Diffusion of Si in liquid Al away from the contact points is identified as the main differentiator to a full‐area Al‐BSF; therefore, a diffusion‐based solution to the involved differential equation is pursued. Data on the Si distribution in the Al and the resulting BSF structures are experimentally obtained by firing samples with different metal contact geometries, peak temperature times and pastes as well as by investigating them by means of scanning electron microscopy and energy dispersive X‐ray spectroscopy. The Si diffusivity in the Al paste is then calculated from these results. It is found that the diffusivity is strongly dependent on the paste composition. Furthermore, the local BSF doping profiles and thicknesses resulting from different contact geometries and paste parameters are calculated from the Si concentration at the contact sites, the diffusivity and solubility data. These profiles are then used in a finite element device simulator to evaluate their performance on solar cell level. With this approach, a beneficial paste composition for any given rear contact geometry can be determined. Two line widths are investigated, and the effects of the different paste properties are discussed in the light of the solar cell results obtained by simulation. Copyright © 2013 John Wiley & Sons, Ltd.

In this work, the solar cell development issues arising by adding a dielectric rear side passivation to a standard screen-printing process are discussed with deposited Al type Cz-Si as an example. The influence of several design parameters is assessed in simulation and experiment and an optimization strategy is presented. These parameters include optical properties of the cell, like the choice of dielectric layer thickness and wafer surface roughness, parameters that influence the passivation quality like the temperature of the co in a belt furnace as well as electrical parameters like contact geometry, contact spacing and base resistivity. Their influence on the three efficiency-determining quantities, V OC outlined. Special attention is paid to minimizing the inevitable loss in FF in a PERC design.Index Terms -dielectric films, finite element methods, photovoltaic cells, semiconductor device manufacture,