T.N. Kost

A new type of high-efficiency bifacial silicon solar cell with external busbars and a current-collecting wire grid

Results regarding bifacial silicon solar cells with external busbars are presented. The cells consist of [n+p(n)p+] Cz-Si structures with a current-collecting system of new design: a laminated grid of wire external busbars (LGWEB). A LGWEB consists of a transparent conducting oxide film deposited onto a Si structure, busbars adjacent to the Si structure, and a contact wire grid attached simultaneously to the oxide and busbars using the low-temperature lamination method. Bifacial LGWEB solar cells demonstrate record high efficiency for similar devices: 17.7%(n-Si)/17.3%(p-Si) with 74–82% bifaciality for the smooth back surface and 16.3%(n-Si)/16.4%(p-Si) with 89% bifaciality for the textured back surface. It is shown that the LGWEB technology can provide an efficiency exceeding 21%.

Effect of conditions of deposition and annealing of indium oxide films doped with fluorine (IFO) on the photovoltaic properties of the IFO/p-Si heterojunction

In2O3:F (IFO) films were deposited onto crystalline silicon and glass by the pyrosol method. The effect of temperature and oxygen in the course of deposition and also of subsequent annealings in various media on the photovoltaic properties of the IFO/Si structure was measured. It is found that IFO forms a rectifying contact to p-Si, makes it possible to obtain a high photovoltage Up = 586 mV and an internal quantum yield higher than 97% for the IFO/(pp+)Si structure, and features a low (0.3–0.4 Ω cm) resistivity. An increase in Up is stimulated by an increase in the temperature of the IFO deposition, a low content of oxygen in the carrier gas, and annealing in argon with methanol vapors. It is concluded that oxygen profoundly affects the surface of the IFO grains and that the transition layer greatly affects the photovoltaic properties of the IFO/(pp+)Si structures.

Effect of the tin content on the composition and optical and electrical properties of ITO films deposited onto silicon and glass by ultrasonic spray pyrolysis

With the aim of optimizing the properties of tin-doped indium oxide (ITO) films as applied to silicon solar cells, ∼100-nm-thick ITO films were deposited onto (nn+)-Cz-Si and glass substrates by ultrasonic spray pyrolysis in argon at a temperature of 380°C. The relative Sn and In content in the film-forming solution was varied in the range of [Sn]/[In] = 0–12 at %. Optimal parameters are exhibited by the films produced at [Sn]/[In] = 2–3 at % in the solution ([Sn]/([In] + [Sn]) = 5.2–5.3 at % in the film). For such films deposited onto glass substrates, the effective absorptance weighted over the solar spectrum in the wavelength range from 300 to 1100 nm is 1.6–2.1%. The sheet resistance Rs of the films deposited onto silicon and glass is, correspondingly, 45–55 and 165–175 Ω▭−1. After eight months of storage in air, the resistance Rs of the optimal films remained unchanged; for the other films, the resistance Rs increased: for the films on silicon and glass, the resistance Rs became up to 2 and 14 times higher, respectively.

Optimization of the deposition and annealing conditions of fluorine-doped indium oxide films for silicon solar cells

Fluorine-doped indium oxide (IFO) films are deposited onto (pp+)Si and (n+nn+)Si structures made of single-crystal silicon by ultrasonic spray pyrolysis. The effect of the IFO deposition time and annealing time in an argon atmosphere with methanol vapor on the IFO chemical composition, the photovoltage and fill factor of the Illumination-Uoc curves of IFO/(pp+)Si structures, and the sheet resistance of IFO/(n+nn+)Si structures, correlating with the IFO/(n+)Si contact resistance, is studied. The obtained features are explained by modification of the properties of the SiOx transition layer at the IFO/Si interface during deposition and annealing. Analysis of the results made it possible to optimize the fabrication conditions of solar cells based on IFO/(pp+)Si heterostructures and to increase their efficiency from 17% to a record 17.8%.

Effect of the temperature during deposition of AlOx films by spray pyrolysis on their passivating properties in a silicon solar cell

The effect of the deposition temperature of AlOx in the range 330–530°C by spray pyrolysis on the rear-surface parameters of silicon (n+pp+)Cz-Si/AlOx solar cells has been studied. It is found that, as the temperature of AlOx deposition is increased, all parameters of the rear surfaces decrease; e.g., the photocurrent density decreases from 25.4 to 24.1 mA/cm2; the photovoltage decreases from 611 to 598 mV; and the efficiency decreases from 12.2 to 10.9%. This indicates that passivation of the p+-type surface with AlOx films becomes less effective. It is concluded that, as the temperature of AlOx deposition is increased, the value of the positive charge incorporated into the nonstoichiometric interphase SiOx layer formed between c-Si and AlOx in the course of AlOx deposition, which brings about screening of the negative charge localized at the AlOx-SiOx interface and, respectively, a decrease in the field-induced passivation, increases.

n-Si bifacial concentrator solar cell

Various approaches have been developed for reducing the cost of the photoelectricity produced by silicon solar cells (SCs). Of highest priority among these approaches are improvement of the efficiency of the SCs, transition from p-Si to n-Si, light concentration, and use of bifacial SCs. In the present study, an SC combining all these approaches has been developed. In this SC, transparent conducting oxides serve as antireflection and passivating electrodes in an indium-tin-oxide/(p+nn+)-Si/indium-fluorine-oxide structure fabricated from Cz-Si with wire contacts (Laminated Grid Cell design). The SC has front/rear efficiencies of 16.5–16.7/15.1–15.3% X (under 1–3 suns). This result is unique because the combination of bifaciality and concentrator operation has no analogs and the SC compares well with the world standard among both bifacial and concentrator SCs.

Laminated grid solar cells (LGCells) on multicrystalline silicon. Application of atomic hydrogen treatment

For the first time, solar cells of laminated grid cell (LGCell) design are fabricated on multicrystalline nontextured silicon (mc-Si). An efficiency of 15.9% is achieved. The effect of (n+pp+)-mc-Si structure treatment by atomic hydrogen generated by a hot filament and microwave plasma is studied. Hydrogenation improves the parameters describing the dependence of the open-circuit voltage on the radiation intensity and the long-wavelength (λ = 1000 nm) sensitivity of the solar cell by 10–20%, which indicates that defects in mc-Si are passivated. Hydrogenation of the emitter side results in an increase in the series resistance of the solar cell, a decrease in the short-wavelength (λ = 400 nm) sensitivity by 30–35%, and the appearance of an oxygen peak in the energy-dispersive spectra (EDS). These effects are eliminated by fine etching of the emitter.

Conversion characteristics of silicon photovoltaic cells for optical beaming

The photoconversions efficiency of powerful collimated coherent single-mode and multimode wave beams with λ= 808 nm and 1064 nm was studied and the experimental results are presented. A set photocells based on silicon with different topological structure is considered including monofacial and bifacial cells, as well as those that have a vertical orientation. Photocell characteristics (short-circuit current Isc, open-circuit voltage, Voc and fillfactor) obtained in the temperature range from 25°C to 50°C and also at a beam power, P, of up to 100 Suns are discussed.

Concentrator bifacial crystalline silicon solar cells with multi-wire metallization attached to TCO layers using transparent conductive polymers

Replacing expensive silver with inexpensive copper for the metallization of silicon wafer solar cells can lead to substantial reductions in material costs associated with cell production. A promising approach is the use of multi-wire design. This technology uses many wires in the place of busbars, and the copper wires are “soldered” during the low-temperature lamination process to the fingers (printed or plated) or to the transparent conductive oxide (TCO) layer, e.g. in the case of the α-Si/c-Si heterojunction cells. Here we describe a solar cell design in which wires are attached to TCO layers using transparent conductive polymer (TCP) films. To this end, we have synthesized a number of thermoplastics, poly(arylene ether ketone) copolymers (co-PAEKs), containing phthalide in their main chain. The fraction of phthalide-containing units in the copolymers was p = 3, 5, 15, and 50 mol %. With increasing p, the peak strain temperature of the co-PAEKs rises from 205 to 290 °C and their optical band gap and re...

Formation of low-reflection multicrystalline silicon surface by laser- induced structuring for application on silicon solar cells

The formation of laser-induced structures on the multicrystalline silicon surface has been investigated. Optimum performances of the surface structurization have been explored. A cardinal decrease in reflectance from modified surface has been discovered in a wide spectral range in comparison with the samples of chemically texturized monocrystalline silicon. The influence of subsequent chemical etching on the reflection spectra of the texturized samples surface has been analyzed.