William J. Dauksher

750 mV open circuit voltage measured on 50 μm thick silicon heterojunction solar cell

This paper presents experimental evidence that silicon solar cells can achieve >750 mV open circuit voltage at 1 Sun illumination providing very good surface passivation is present. 753 mV local open circuit voltage was measured on a 50 μm thick non-metalized silicon heterojunction solar cell. The paper also considers a recombination model at open circuit based on the recent Auger and radiative recombination parameterization and the measured surface saturation current density. The loss mechanisms at open circuit and several practical pathways to achieve >760 mV open circuit voltage in silicon heterojunction solar cells are discussed.

Surface passivation of n-type c-Si wafers by a-Si/SiO2/SiNx stack with <1 cm/s effective surface recombination velocity

The passivation quality of an a-Si/SiO2/SiNx (aSON) stack deposited by conventional PECVD at 60 ms on 5000 Ω-cm and 20.9 ms on 1.7 Ω-cm mirror polished float zone (FZ) material passivated with aSON stacks.

Manipulation of K center charge states in silicon nitride films to achieve excellent surface passivation for silicon solar cells

High quality surface passivation (Seff  ±8 × 1012 cm−2) into a dual layer stack of Plasma Enhanced Chemical Vapor Deposition (PECVD) Silicon Nitride (SiNx)/PECVD Silicon Oxide (SiO2) films using a corona charging tool. We demonstrate long term stability and uniform charge distribution in the SiNx film by manipulating the charge on K center defects while negating the requirement of a high temperature thermal oxide step.

A simplified process flow for silicon heterojunction interdigitated back contact solar cells: Using shadow masks and tunnel junctions

A novel process flow, which can allow the formation of interdigitated p- and n-type a-Si strips and corresponding transparent conductive oxide (TCO) and metal layers for silicon heterojunction interdigitated back contact (SHJ-IBC) solar cells using only a single alignment step and without using any resist patterning is presented. The flow is based on the deposition of a-Si, TCO and metal layers through a stack of shadow masks. Three variation of the flow are described. Several key process components to include a-Si deposition and H2 plasma etch through the shadow mask are demonstrated and described.

Development of Cu plating for silicon heterojunction solar cells

This paper reports the results of the study comparing various patterning and plating methods for the deposition of Cu electrodes on transparent conductive oxides for silicon heterojunction solar cells. We compared direct electroplating of Cu on different metal seeds (Ag, Ni, Cr and Ti deposited on transparent conductive oxide by physical vapor deposition) to the light induced plating of Ni/Cu directly on transparent conductive oxide. Patterning was done either using photoresists (formed by spin-on, screen printing or lamination) or lift-off of the PECVD dielectric using screen printed resist. The geometry of the fingers, line resistance, contact resistance and adhesion were used as comparative parameters. We identified direct electroplating of Cu on the sputtered Ag seed to achieve the lowest contact resistance and the best adhesion. All photoresists were able to achieve less than 60 micron resolution and could produce the fingers with the sought height (some, however, having a characteristic mushroom shape). The best silicon heterojunction cell with Cu contacts directly electroplated on the sputtered Ag seed achieved 21.9% efficiency on 153 cm2 area.

High open-circuit voltages on thin silicon solar cells

Silicon heterostructures solar cells have very low surface recombination and the resulting cells can achieve high open circuit voltages. We have demonstrated an open circuit voltage for a silicon solar cell at 753 mV. We show high lifetimes on textured substrates with an average of 3 ms using thin layers of doped and intrinsic amorphous silicon and that the lifetimes are consistent across batches. We show that for high measured lifetimes there is a close match between the Implied VOC (measured from photoconductance) and the Actual VOC (as measured on a final cell). Recent measurements with have produced Implied VOCs of 761 mV on textured substrates.