X. Niquille

High-Stable-Efficiency Tandem Thin-Film Silicon Solar Cell With Low-Refractive-Index Silicon-Oxide Interlayer

We report the recent advances and key requirements for high-efficiency “micromorph” tandem thin-film silicon solar cells composed of an amorphous silicon top cell and a microcrystalline silicon bottom cell. The impact of inserting a low-refractive-index silicon-oxide (SiOx) film as intermediate reflecting layer (IRL) is highlighted. We show that refractive indexes as low as 1.75 can be obtained for layers still conducting enough to be implemented in solar cells, and without no additional degradation. This allows for high top-cell current densities with thin top cells, enabling low degradation rates. A micromorph cell with a certified efficiency of 12.63% (short-circuit current density of 12.8 mA/cm2) is obtained for an optimized stack. Furthermore, short-circuit current densities as high as 15.9 mA/cm2 are reported in the amorphous silicon top-cell of micromorph devices by combining a 150-nm-thick SiOx-based IRL and a textured antireflecting coating at the air-glass interface.

N/I buffer layer for substrate microcrystalline thin film silicon solar cell

The influence of the substrate surface morphology on the performance of microcrystalline silicon solar cells in the substrate or n-i-p (nip) configuration is studied in this paper. The experiments are carried out on glass substrates coated with naturally textured films of ZnO deposited by low pressure chemical vapor deposition which serves as backcontact and as template for the light trapping texture. The film surface morphology can be modified with a plasma treatment which smoothens the V-shaped valleys to a more U- shaped form. We investigate, first, the influence of different substrates morphologies on the performance of microcrystalline (μc-Si:H) thin film silicon solar cells deposited by very high frequency plasma enhanced chemical vapor deposition. The V-shaped morphologies are found to have strong light trapping capabilities but to be detrimental for the μc-Si:H material growth and lead to degraded open circuit voltage (Voc) and fill factor (FF) of the solar cells. Hence, in Sec., we introduce a buffer layer with a higher amorphous fraction between the n doped and intrinsic layer. Our study reveals that the buffer layer limits the formation of voids and porous areas in the μc- Si:H material on substrates with strong light trapping capabilities. Indeed, this layer mitigates Voc and FF losses which enhances the performance of the μc-Si:H solar cell. Finally, by applying our findings, we report an efficiency of 9% for a nip μc-Si:H thin film silicon cell with a thickness of only 1.2 μm.

Light-induced degradation of thin film amorphous and microcrystalline silicon solar cells

Absorption spectra of two dilution series of microcrystalline solar cells deposited by VHF-PECVD were measured by FTPS. The dilution series were composed of pin and of nip cells, with i-layers ranging from highly crystalline to mainly amorphous. This paper evaluates stability of the cells when exposed to white light (AM 1.5-like spectrum). Defect-related absorption is minimum for cells of medium crystallinity (deposited in the transition region); but is increased for theses cells by a factor 2 to 4 under light-soaking. It still remains lower than that of highly crystalline cells which show very little degradation. Variation of electrical parameters is also investigated as a function of light soaking and annealing steps. Cells of medium crystallinity show approximately 10% reversible relative efficiency loss after 1000 hours of light soaking.

Zinc tin oxide as high-temperature stable recombination layer for mesoscopic perovskite/silicon monolithic tandem solar cells

Perovskite/crystalline silicon tandem solar cells have the potential to reach efficiencies beyond those of silicon single-junction record devices. However, the high-temperature process of 500 °C needed for state-of-the-art mesoscopic perovskite cells has, so far, been limiting their implementation in monolithic tandem devices. Here, we demonstrate the applicability of zinc tin oxide as a recombination layer and show its electrical and optical stability at temperatures up to 500 °C. To prove the concept, we fabricate monolithic tandem cells with mesoscopic top cell with up to 16% efficiency. We then investigate the effect of zinc tin oxide layer thickness variation, showing a strong influence on the optical interference pattern within the tandem device. Finally, we discuss the perspective of mesoscopic perovskite cells for high-efficiency monolithic tandem solar cells.

Silicon-Rich Silicon Carbide Hole-Selective Rear Contacts for Crystalline-Silicon-Based Solar Cells

The use of passivating contacts compatible with typical homojunction thermal processes is one of the most promising approaches to realizing high-efficiency silicon solar cells. In this work, we investigate an alternative rear-passivating contact targeting facile implementation to industrial p-type solar cells. The contact structure consists of a chemically grown thin silicon oxide layer, which is capped with a boron-doped silicon-rich silicon carbide [SiCx(p)] layer and then annealed at 800-900 °C. Transmission electron microscopy reveals that the thin chemical oxide layer disappears upon thermal annealing up to 900 °C, leading to degraded surface passivation. We interpret this in terms of a chemical reaction between carbon atoms in the SiCx(p) layer and the adjacent chemical oxide layer. To prevent this reaction, an intrinsic silicon interlayer was introduced between the chemical oxide and the SiCx(p) layer. We show that this intrinsic silicon interlayer is beneficial for surface passivation. Optimized passivation is obtained with a 10-nm-thick intrinsic silicon interlayer, yielding an emitter saturation current density of 17 fA cm-2 on p-type wafers, which translates into an implied open-circuit voltage of 708 mV. The potential of the developed contact at the rear side is further investigated by realizing a proof-of-concept hybrid solar cell, featuring a heterojunction front-side contact made of intrinsic amorphous silicon and phosphorus-doped amorphous silicon. Even though the presented cells are limited by front-side reflection and front-side parasitic absorption, the obtained cell with a Voc of 694.7 mV, a FF of 79.1%, and an efficiency of 20.44% demonstrates the potential of the p+/p-wafer full-side-passivated rear-side scheme shown here.

Periodic textures for enhanced current in thin film silicon solar cells

Note: IMT-NE Number: 481 Reference PV-LAB-CONF-2008-002 Record created on 2009-02-10, modified on 2017-05-10

Hot Embossing of Polymer Substrates for Thin Silicon Cell Applications

The use of polymer substrates for thin film solar cells is becoming an issue of great interest, as they facilitate monolithic interconnection of the cells to produce modules and can be used in continuous roll-to-roll processes. However, to reach high efficiencies of thin film silicon cells on polymer substrates, the development of efficient light confinement strategies has to be improved. In this work, hot embossing is used to produce a suitable surface morphology on PEN substrates. Three morphologies have been studied by using three selected masters. To evaluate the quality of the embossing, the morphology of the masters and that of the stamped PEN samples have compared. Finally, the stamped polymers have been covered with thin Ag and transparent conductive oxide (TCO) layers and whole reflectance experiments have been performed to asses the efficiency of the fabricated back reflectors

Optical developments for silicon thin film solar cells in the substrate configuration

Note: IMT-NE Number: 483 Reference PV-LAB-CONF-2008-003 Record created on 2009-02-10, modified on 2017-05-10

Towards Microcrystalline Silicon n-i-p Solar Cells with 10% Conversion Efficiency

Note: IMT-NE Number: 361 Reference PV-LAB-CONF-2003-001 Record created on 2009-02-10, modified on 2017-05-10