Silicon Single-junction Solar Cells Research Articles

Noise and optical spectroscopy of single junction silicon solar cell

Noise and optical spectroscopy of single junction silicon solar cell

Low temperature perovskite solar cells with an evaporated TiO2 compact layer for perovskite silicon tandem solar cells

Silicon-based tandem solar cells can overcome the efficiency limit of single junction silicon solar cells. Perovskite solar cells are particularly promising as a top cell in monolithic tandem devices due to their rapid development towards high efficiencies, a tunable band gap with a sharp optical absorption edge and a simple production process. In monolithic tandem devices, the perovskite solar cell is deposited directly on the silicon cell, requiring low-temperature processes (< 200°C) to maintain functionality of under-lying layers of the silicon cell in case of highly efficient silicon hetero-junction (SHJ) bottom solar cell. In this work, we present a complete low-temperature process for perovskite solar cells including a mesoporous titanium oxide (TiO2) scaffold - a structure yielding the highest efficiencies for single-junction perovskite solar cells. We show that evaporation of the compact TiO2 hole blocking layer and ultra-violet (UV) curing for the mesoporous TiO2 layer allows for good performance, comparable to high-temperature (> 500°C) processes. With both manufacturing routes, we obtain short-circuit current densities (JSC) of about 20 mA/cm², open-circuit voltages (VOC) over 1 V, fill factors (FF) between 0.7 and 0.8 and efficiencies (η) of more than 15%. We further show that the evaporated TiO2 layer is suitable for the application in tandem devices. The series resistance of the layer itself and the contact resistance to an indium doped tin oxide (ITO) interconnection layer between the two sub-cells are low. In addition, the low parasitic absorption for wavelengths above the perovskite band gap allow a higher absorption in the silicon bottom solar cell, which is essential to achieve high tandem efficiencies.

In situ growth of Sb2S3 thin films by reactive sputtering on n-Si(100) substrates for top sub-cell of silicon based tandem solar cells

Si-based tandem solar cells have emerged as a promising alternative to replace the current high efficiency silicon single junction solar cells. Sb2S3 is a promising candidates for top cell absorbers due to its suitable band gap, non-toxic and earth-abundant constituent, simple composition, and long term stability. Here, in situ growth of Sb2S3 thin films by radio frequency (RF) reactive sputtering on n-Si(100) substrates is reported. The effects of the growth temperature on morphology, structure, optical and electrical properties of the films were evaluated. The top sub-cell device shows an open circuit voltage (Voc) of 367mV, indicating the potential to be the top cell of the next generation Si-based tandem solar cells.

Light-trapping design for thin-film silicon-perovskite tandem solar cells

Using finite-difference time-domain simulations, we investigate the optical properties of tandem silicon/perovskite solar cells with a photonic crystal architecture, consisting of a square-lattice array of inverted pyramids with a center-to-center spacing of 2.5 μm. We demonstrate that near-perfect light-trapping and absorption can be achieved over the 300–1100 nm wavelength range with this architecture, using less than 10 μm (equivalent bulk thickness) of crystalline silicon. Using a one-diode model, we obtain projected efficiencies of over 30% for the two-terminal tandem cell under a current-matching condition, well beyond the current record for single-junction silicon solar cells. The architecture is amenable to mass fabrication through wet-etching and uses a fraction of the silicon of traditional designs, making it an attractive alternative to other silicon-perovskite tandem designs.

Photovoltaic cells energy performance enhancement with down-converting photoluminescence phosphors

Summary Phosphors, synthesized by the urea homo-precipitation method, were examined as ultraviolet-spectral down conversion materials for improving the light absorption and electrical characteristics of commercial single-junction silicon solar cells. The photovoltaic (PV) cells were coated with erbium and terbium doped gadolinium oxysulfide phosphors encapsulated in ethyl vinyl-acetate binder using blade screen printing technique, and the optimum concentration of phosphor in the composite resulted in the largest light conversion, and superior electrical output and energy transfer efficiency. Moreover, the results demonstrated that the composition of dispersed phosphors has a strong influence on the amount of ultraviolet-light converted and electron transition capacity of PV cells. The experimental results showed in an optimized PV cell, an enhancement of 0.54% (from 12.11% to 12.65%) in the energy conversion of a Si-based PV cell was achieved. Copyright © 2015 John Wiley & Sons, Ltd.

Photovoltaic cells energy performance enhancement with down-converting photoluminescence phosphors

Phosphors, synthesized by the urea homo-precipitation method, were examined as ultraviolet-spectral down conversion materials for improving the light absorption and electrical characteristics of commercial single-junction silicon solar cells. The photovoltaic (PV) cells were coated with erbium and terbium doped gadolinium oxysulfide phosphors encapsulated in ethyl vinyl-acetate binder using blade screen printing technique, and the optimum concentration of phosphor in the composite resulted in the largest light conversion, and superior electrical output and energy transfer efficiency. Moreover, the results demonstrated that the composition of dispersed phosphors has a strong influence on the amount of ultraviolet-light converted and electron transition capacity of PV cells. The experimental results showed in an optimized PV cell, an enhancement of 0.54% (from 12.11% to 12.65%) in the energy conversion of a Si-based PV cell was achieved. Copyright © 2015 John Wiley & Sons, Ltd.

Toward the Practical Limits of Silicon Solar Cells

This paper reports recent efficiency results achieved by SunPower (SPWR) using industrially relevant manufacturing processes and then reexamines the following age-old question: “What efficiency can a single-junction Silicon solar cell suited to large-scale manufacturing achieve?” Through examination of a gap analysis of the SPWR cell and use of other relevant proof-points, insights are provided into the remaining challenges to achieving the practical limits.

Characterization of solar cells by thermal transient testing

The current paper deals with the application of thermal transient testing as a characterization tool for solar modules. Based on the measurement of different samples (concentrator solar cell, single junction silicon solar cell) we prove the applicability of this measurement technique and address some specific issues of the characterization of solar cells by the thermal transient method.From the measurement metrics such as junction-to-base plate thermal resistance and thermal capacitance(s) can be derived and can serve as a basis of a multi domain solar cell model. The used technique also enables us to verify the quality of attachment layers in a solar module allowing fair quality control and reliability analysis of these devices. Finally a method is proposed to regain the data that is covered by the initial electric transient following the power step. This initial electric transient can be high in large surface devices like solar cells, and covers valuable data describing the structure near to the p–n junction. To eliminate this, simulated transients were fitted to the part of the actual measured thermal transient where the electric transient already decayed. This way the part of the thermal transient that was covered by the electric transient can be reconstructed.

Development of plasma-enhanced chemical vapor deposition microcrystalline silicon oxide as a replacement for N-type or back transparent conducting oxide layers in amorphous silicon single-junction solar cells

The n-type hydrogenated microcrystalline silicon oxide (μc-SiOx:H(n)) thin films with varied electrical and optical properties were prepared. We employed μc-SiOx:H(n) as a replacement for n-type hydrogenated amorphous silicon (a-Si:H(n)) or back transparent conducting oxide (TCO) layers in hydrogenated amorphous silicon (a-Si:H) single-junction solar cells. Compared to the standard cell with a-Si:H(n)/ITO/Ag back reflecting structure, the cell using a-Si:H(n)/μc-SiOx:H(n)/Ag or μc-SiOx:H(n)/Ag showed a similar or even better performance. This improvement of cell performance mainly arose from the increased short-circuit current density (JSC) that originated from the increased long wavelength (580–660 nm) absorption in the absorber confirmed by the quantum efficiency measurement. The “all plasma-enhanced chemical vapor deposition ” (if the front TCO and metal contact are disregarded) process without TCO (indium tin oxide, ITO) sputtering can simplify the fabrication and result in better interface quality. Compared to the standard cell, the conversion efficiency of a-Si:H cells using an 80 nm thick μc-SiOx:H(n)/Ag back reflecting structure was enhanced from 9.32% to 9.84%, with VOC = 0.90 V, JSC = 14.84 mA/cm2, and FF = 73.7%.

Fabrication of solution-processed hydrogenated amorphous silicon single-junction solar cells

Hydrogenated amorphous silicon solar cells were fabricated using solution-based processes. All silicon layers of the p-i-n junction were stacked by a spin-cast method using doped and non-doped polydihydrosilane solutions. Further, a hydrogen-radical treatment under vacuum conditions was employed to reduce spin density in the silicon films. Following this treatment, the electric properties of the silicon films were improved, and the power conversion efficiency of the solar cells was also increased from 0.01% to 0.30%–0.51% under the AM-1.5G (100 mW/cm2) illumination conditions.

Design and application of dielectric distributed Bragg back reflector in thin-film silicon solar cells

A dielectric distributed Bragg reflector (DBR) formed by four pairs of hydrogenated amorphous silicon/silicon nitride layers is used as the back reflector in thin-film silicon solar cells. The DBR was designed to perform in a broad wavelength range with the peak reflectance at 600nm. The DBR was fabricated at low substrate temperature (172°C) and applied at the rear side of flat and textured amorphous silicon single-junction solar cells in both superstrate (pin) and substrate (nip) configurations. The spectral response and electrical I–V characteristics were measured. Solar cells with optimized DBR exhibit an enhanced external quantum efficiency in the long wavelength range and the electrical performance is comparable to solar cells having conventional Ag back reflector.

Novel etching method on high rate ZnO:Al thin films reactively sputtered from dual tube metallic targets for silicon-based solar cells

Highly transparent and conductive aluminum-doped zinc oxide thin films (ZnO:Al) were reactively sputtered from metallic targets at high rate of up to 90 nm m/min. For the application as transparent light scattering front contact in silicon thin film solar cells, a texture etching process is applied. Typically, it is difficult to achieve appropriate etch features in hydrochloric acid as the deposition process must be tuned and the interrelation is not well understood. We thus introduce a novel two-step etching method based on hydrofluoric acid. By tuning the etch parameters we varied the surface morphology and achieved a regular distribution of large craters with the feature size of 1–2 μm in diameter and about 250 nm in depth. Microcrystalline silicon single junction solar cells (μc-Si:H) and amorphous/microcrystalline silicon (a-Si:H/μc-Si:H) tandem solar cells with high efficiency of up to 8.2% and 11.4%, respectively, were achieved with optimized ZnO:Al films as light scattering transparent front contact.

Productivity potential of an inline deposition system for amorphous and microcrystalline silicon solar cells

Amorphous and microcrystalline silicon single layers and p–i–n solar cells were produced dynamically using an inline deposition system called “line source”. A highly uniform deposition of thin-film silicon layers with layer-thickness variations of less than ±5% was achieved. Amorphous and microcrystalline silicon single junction solar cells were dynamically fabricated with initial efficiencies of 8.3% and 6.3%, respectively. The dynamic deposition rate of these solar cells is 6.75 nm m/min in case of a-Si:H and 3.3 nm m/min for μc-Si:H. In this work it will be shown that an enhancement of the deposition rate up to 15.6 nm m/min during the i-layer deposition of a-Si:H solar cells has only a weak negative influence on the initial efficiencies of the cells. Further on, the effect of substrate velocity on solar cell characteristics of a-Si:H solar cells is investigated. Finally, a productivity estimation of the line source concept is presented.

Potential of light trapping in microcrystalline silicon solar cells with textured substrates

AbstractThe real and potential benefits of light trapping in microcrystalline silicon single‐junction solar cells are studied theoretically. Effects of a hypothetical high haze parameter of textured transparent conductive oxide on quantum efficiency and short‐circuit current of the solar cell are analysed by numerical simulation. The role of the angular distribution function of scattered light as a second important scattering parameter is shown. The potential thickness reductions of the intrinsic layer due to enhanced light trapping are demonstrated. Copyright © 2003 John Wiley &amp; Sons, Ltd.