n-i-p Nanocrystalline Hydrogenated Silicon Solar Cells with RF-Magnetron Sputtered Absorbers

Nanocrystalline hydrogenated silicon (nc-Si:H) substrate configuration n-i-p solar cells have been fabricated on soda lime glass substrates with active absorber layers prepared by plasma enhanced chemical vapor deposition (PECVD) and radio frequency magnetron sputtering. The cells with nanocrystalline PECVD absorbers and an untextured back reflector serve as a baseline for comparison and have power conversion efficiency near 6%. By comparison, cells with sputtered absorbers achieved efficiencies of about 1%. Simulations of external quantum efficiency (EQE) are compared to experimental EQE to determine a carrier collection probability gradient with depth for the device with the sputtered i-layer absorber. This incomplete collection of carriers generated in the absorber is most pronounced in material near the n/i interface and is attributed to breaking vacuum between deposition of layers for the sputtered absorbers, possible low electronic quality of the nc-Si:H sputtered absorber, and damage at the n/i interface by over-deposition of the sputtered i-layer during device fabrication

Amorphous, Polymorphous, and Microcrystalline Silicon Thin Films Deposited by Plasma at Low Temperatures

The present chapter is devoted to the study of amorphous (a-Si:H), polymorphous (pm-Si:H), and microcrystalline (μc-Si:H) silicon, deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique at low temperatures. We have studied the main deposition parameters that have strong influence on the optical, electrical, and structural properties of the polymorphous and microcrystalline materials. Our results reveal the key deposition conditions for obtained films with optical and electrical characteristics, which are suitable for applications on thin-film solar cells and semiconductor devices

Industrialization of Hot Wire Chemical Vapor Deposition for thin film applications

AbstractThe consequences of implementing a Hot Wire Chemical Vapor Deposition (HWCVD) chamber into an existing in-line or roll-to-roll reactor are described. The hardware and operation of the HWCVD production reactor is compared to that of existing roll-to-roll reactors based on Plasma Enhanced Chemical Vapor Deposition. The most important consequences are the technical consequences and the economic consequences, which are both discussed. The technical consequences are adaptations needed to the hardware and to the processing sequences due to the different interaction of the HWCVD process with the substrate and already deposited layers. The economic consequences are the reduced investments in radio frequency (RF) supplies and RF components. This is partially offset by investments that have to be made in higher capacity pumping systems. The most mature applications of HWCVD are moisture barrier coatings for thin film flexible devices such as Organic Light Emitting Diodes and Organic Photovoltaics, and passivation layers for multicrystalline Si solar cells, high mobility field effect transistors, and silicon heterojunction cells (also known as heterojunction cells with intrinsic thin film layers). Another example is the use of Si in thin film photovoltaics. The cost perspective per unit of thin film photovoltaic product using HWCVD is estimated at 0.07€/Wp for the Si thin film component

High‐Density Plasma‐Enhanced Chemical Vapor Deposition of Si‐Based Materials for Solar Cell Applications

High‐quality and low‐cost fabrication of Si‐based materials, in which many fundamental and technology problems still remain, have attracted tremendous interests due to their wide applications in solar cell area. Low‐frequency inductively coupled plasma (LFICP) provides a new and competitive solution, thanks to its inherent advantages of high‐density plasma, low sheath potential, and low electron temperature, etc. The plasma characteristic‐dependent microstructures, optical and electronic properties of the LFICP CVD‐based hydrogenated amorphous/microcrystalline silicon and silicon oxides are systematically studied. Remote‐LFICP combing the high‐density plasma nature of ICP and mild ion bombardment on growing surface in remote plasma allows the deposition of high‐quality Si‐based materials providing excellent c‐Si surface passivation. The mechanism of surface passivation by LFICP CVD Si‐based materials, interaction between plasma species and growing surface are analyzed in terms of the plasma properties. These results pave the way for LFICP CVD utilization in Si‐based high‐efficiency and low‐cost solar cell fabrication

Low Temperature Plasma Synthesis of Nanocrystals and their Application to the Growth of Crystalline Silicon and Germanium Thin Films

International audienceWe summarize our research studies on the synthesis of silicon and germanium nanocrystals and their application to the growth of a variety of thin films, spanning the range from fully disordered amorphous up to fully ordered crystalline. All these films are deposited in a standard radio-frequency glow discharge system at low temperature (~200 °C). We show how the plasma synthesis of silicon nanocrystals, initially a side effect of powder formation, has become over the years an exciting field of research which has opened the way to new opportunities in the field of materials deposition and their application to optoelectronic devices. Our results suggest that epitaxy requires the melting/amorphization of the nanocrystals upon impact on the substrate, the subsequent epitaxial growth being favored on (100) c-Si substrates. As a consequence, the control of the impact energy is a critical aspect of the growth which will require new strategies such as the use of tailored voltage waveforms

Hybrid Silicon-Organic Heterojunction Structures for Photovoltaic Applications

The concept for inorganic-organic device is an attractive technology to develop devices with better characteristics and functionality due to the complementary advantages of inorganic and organic materials. This chapter provides an overview of the principal requirements for organic and inorganic semiconductor properties and their fabrication processes and focus on the compatibility between low temperature plasma enhanced chemical vapor deposition (PECVD) and polymer organic materials deposition. The concept for inorganic-organic device was validated with the fabrication of three hybrid thin film photovoltaic structures, based on hydrogenated silicon (Si:H), organic poly(3-hexythiophene): methano-fullerenephenyl-C61-butyric-acid-methyl-ester (P3HT:PCBM), and poly(3,4ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) films. Optoelectronic characteristics, performance characteristics, and interfaces of the different configurations aspects are discussed. Hybrid ITO/PEDOT:PSS/(i)Si:H/(n)Si:H structure results in a remarkably high short circuit current density as large as 17.74 mA/cm2, which is higher than the values in organic or inorganic reference samples. Although some hybrid structures demonstrated substantial improvement of performance, other hybrid structures showed poor performance, further R&D efforts seem to be promising, and should be focused on deeper study of organic materials and related interface properties

Fabrication and characterization of microcrystalline silicon solar cells

In this study, single junction p-i-n μc-Si:H solar cells were prepared using plasma of silane diluted by hydrogen in a low-cost, single chamber, non-load-locked RF-PECVD system. Direct structural characterization of μc-Si:H solar cells, rather than stand-alone films, was conducted using Raman Spectroscopy, XRD, and AFM. Strong correlations among device deposition, i-layer structural properties, and device performance have been established. With such correlations, critical issues in fabricating low-cost, large-scale, high performance μc-Si:H solar cells were identified. The critical importance of seeding processes in determining the microstructure of μc-Si:H i-layers and performance of μc-Si:H solar cells has been demonstrated. Using p-layer seeding methods, stable conversion efficiencies of 5% have been achieved using very simple device configuration. Micro-crystallinity obtained from Raman scattering, presented as Ic/Ia, proved to be sensitive to the microstructure of μc-Si:H i-layers. Strong spatial non-uniformity of i-layer microstructure as well as variations in device performance were observed. A wide variety of i-layer microstructures, from mixed-phase Si:H to highly crystalline μc-Si:H, were revealed by Raman scattering. Generally, solar cells with mixed-phase Si:H i-layers exhibit high open circuit voltages, low fill factors, low efficiencies, and severe light-induced degradation. On the other hand, solar cells with truly μc-Si:H i-layers show low open circuit voltages, high fill factors, high efficiencies, and excellent stability against light-induced degradation. It was shown by XRD experiments that high performance, optimum μc-Si:H solar cells exhibit smaller grain sizes compared to solar cells with i-layers showing higher micro-crystallinity. Correlations among non-uniformity pattern, i-layer micro-crystallinity, and AFM surface morphologies were also observed. Solar cells with truly μc-Si:H i-layers exhibit excellent stability under both conventional and accelerated light soaking. Mixed-phase Si:H solar cells show much worse stability against light exposure. However, it has been demonstrated that stable, high performance μc-Si:H solar cells can only be obtained with i-layers being μc-Si:H, yet close to the μc-Si:H to mixed-phase Si:H transition edge where an optimum microcrystallinity range (Ic/Ia at around 1.8) was identified. These optimum μc-Si:H solar cells exhibit moderate open circuit voltages at 0.5 V, high fill factors, high efficiencies, and excellent stability against light-induced degradation. Such optimum μc-Si:H i-layers demand a very narrow optimum processing window

Doping of amorphous and microcrystalline silicon films deposited at low substrate temperatures by hot-wire chemical vapor deposition

The gas phase doping of amorphous (alpha -Si:H) and microcrystalline (muc-Si:H) silicon thin films deposited at substrate temperatures of 25 degreesC and 100 degreesC by hot-wire chemical vapor deposition is studied. Phosphine was used for n-type doping and diborane for p-type doping. The electronic and structural properties of the doped films are studied as functions of hydrogen dilution. Films were deposited on glass and polyethylene terephthalate. Similar dark conductivities, sigma (d), were obtained for the doped films deposited on either substrate. sigma (d) above 10(-6) Omega (-1) cm(-1) were obtained for a-Si:H films doped n-type at 25 degreesC and 100 degreesC (sigma (d)> 10(-4) Omega (-1) cm(-1)) and for alpha -Si:H doped p-type only at 100 degreesC. sigma (d), equal or above 10(-1) Omega (-1) cm(-1), were obtained for muc-Si:H doped p-type at 25 degreesC and 100 degreesC for Ac-Si:H doped n-type. only at 100 degreesC. Isochronal annealing at temperatures up to 200 degreesC reveals that, while the dopants are fully activated in microcrystalline samples, they are only partially activated in amorphous films deposited at a low substrate temperature.Fundação para a Ciência e Tecnologia (FCT) University of Minho (UM