With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

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High-efficiency crystalline silicon solar cells: status and perspectives

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Graphene Materials and Their Use in Dye-Sensitized Solar Cells

A photovoltaic cell comprising a wafer comprising a semiconductor material of a first conductivity type, the wafer comprising a first light receiving surface and a second surface opposite the first surface; a first passivation layer positioned over the first surface of the wafer; a first electrical contact comprising point contacts positioned over the second surface of the wafer and having a conductivity type opposite to that of the wafer; and a second electrical contact comprising point contacts and positioned over the second surface of the wafer and separated electrically from the first electrical contact and having a conductivity type the same as that of the wafer.

Back-contact photovoltaic cells

Plasma-enhanced atomic layer deposition of cobalt oxide onto nanotextured p+n-Si devices enables efficient photoelectrochemical water oxidation and effective protection of Si from corrosion at high pH (pH 13.6). A photocurrent density of 17 mA/cm2 at 1.23 V vs RHE, saturation current density of 30 mA/cm2, and photovoltage greater than 600 mV were achieved under simulated solar illumination. Sustained photoelectrochemical water oxidation was observed with no detectable degradation after 24 h. Enhanced performance of the nanotextured structure, compared to planar Si, is attributed to a reduced silicon oxide thickness that provides more intimate interfacial contact between the light absorber and catalyst. This work highlights a general approach to improve the performance and stability of Si photoelectrodes by engineering the catalyst/semiconductor interface.

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Efficient and sustained photoelectrochemical water oxidation by cobalt oxide/silicon photoanodes with nanotextured interfaces.

https://hal.archives-ouvertes.fr/hal-01706842/document

Study of the composition of hydrogenated silicon nitride SiNx:H for efficient surface and bulk passivation of silicon

Devices, solar cell structures, and methods of fabrication thereof, are disclosed. Briefly described, one exemplary embodiment of the device, among others, includes: a co-fired p-type silicon substrate, wherein the bulk lifetime is about 20 to 125 μs; an n+ layer formed on the top-side of the p-silicon substrate; a silicon nitride anti-reflective (AR) layer positioned on the top-side of the n+ layer; a plurality of Ag contacts positioned on portions of the silicon nitride AR layer, wherein the Ag contacts are in electronic communication with the n+-type emitter layer; an uniform Al back-surface field (BSF or p+) layer positioned on the back-side of the p-silicon substrate on the opposite side of the p-type silicon substrate as the n+ layer; and an Al contact layer positioned on the back-side of the Al BSF layer. The device has a fill factor (FF) of about 0.75 to 0.85, an open circuit voltage (VOC) of about 600 to 650 mV, and a short circuit current (JSC) of about 28 to 36 mA/cm2.

Silicon solar cells and methods of fabrication

Ion-implanted, screen-printed, high-efficiency, stable, n-base silicon solar cells fabricated from readily available 156-mm pseudosquare Czochralski wafers are described, along with prototype modules assembled from such cells. Two approaches are presented. The first approach, which involves a single phosphorus implant, has been used to produce cells (239 cm2) having a tight distribution of Jsc, Voc, and fill factor over a wide range of wafer resistivity (factor of 10), with Fraunhofer-certified efficiencies up to 18.5%. In spite of the full screen-printed and alloyed Al back, a method has been developed to solder such cells in a module. The second approach, which involves implanting both phosphorus for back-surface field (BSF) and boron for front emitter, has been used to produce n-base cells having local back contacts and dielectric (SiNx/SiO2) surface passivation. Efficiencies up to 19.1%, certified by Fraunhofer, have been realized on 239-cm2 cells. A method is also presented to express recombination activity in the cell base as a component of total reverse saturation current density. This allows recombination activity in all three regions of the cell (n+ region and its surface, n-base, and p+ region and its surface) to be compared as components of the total cell J0 to aid in maximizing Voc.

N-Type, Ion-Implanted Silicon Solar Cells and Modules

The effectiveness of manufacturable gettering and passivation technologies is investigated for their ability to improve the quality of a promising Si photovoltaic material. The results of this study indicate that a lifetime enhancement of 30 μs is attained when a backside screen-printed aluminum layer and a thin film of SiNx, applied by plasma-enhanced chemical vapor deposition (PECVD), are simultaneously annealed at 850°C in a lamp-heated belt furnace. Based on the results of this study, a model is proposed to describe the Al-enhanced SiNx induced hydrogen defect passivation in String Ribbon silicon due to the simultaneous anneal. According to this model, three factors play an important role: i) the release of hydrogen from the SiNx film into the substrate; ii) the retention of hydrogen at defect sites in silicon; and iii) the generation of vacancies at the Al−Si interface due to the alloying process which increases the incorporation of hydrogen and creates a chemical potential gradient which enhances the migration of hydrogen in the substrate. A PC1D device simulation indicates that screen-printed cell efficiencies approaching 16% can be achieved if the gettering and passivation treatments examined in this study are employed, the substrate thickness is reduced, and a high-quality surface passivation scheme is applied.

Al-enhanced PECVD SiN x induced hydrogen passivation in string ribbon silicon

Solar cell device having amorphous silicon layers

This paper shows the results and the limitations of a 21% N-Cz 239-cm2 screen-printed cell with blanket p+ emitter and n+ back surface field. In addition, we show the properties and impact of tunnel oxide capped with doped n+ polysilicon and metal on the back side, which can overcome those limitations. Since both the doped n+ layer and the metal contact are outside the bulk silicon wafer, the Jo is dramatically reduced, resulting in much higher $V_{{\rm oc}}$ . Process optimization has resulted in high $iV_{{\rm oc}}$ of  728 mV on symmetric structures. The unmetallized cell structure with Al2O3/SiN passivated lightly doped p+ emitter and a tunnel oxide/n+ poly back also gave high $iV_{{\rm oc}}$ of 734 mV. The finished screen-printed 132-cm2 device gave a $V_{{\rm oc}}$ of 683 mV, $J_{{\rm sc}}$ of 39.4 mA/cm2, FF of 77.6%, and an efficiency of 20.9%. Cell analysis show that implementation of a selective emitter can give higher efficiency.

Vijay Yelundur

Papers

Silicon solar cells and methods of fabrication

N-Type, Ion-Implanted Silicon Solar Cells and Modules

Al-enhanced PECVD SiN x induced hydrogen passivation in string ribbon silicon

Solar cell device having amorphous silicon layers

Ion-Implanted Screen-Printed n-Type Solar Cell With Tunnel Oxide Passivated Back Contact