Ian Marius Peters

The realistic energy yield potential of GaAs-on-Si tandem solar cells: a theoretical case study.

Si based tandem solar cells represent an alternative to traditional compound III-V multijunction cells as a promising way to achieve high efficiencies. A theoretical study on the energy yield of GaAs on Si (GaAs/Si) tandem solar cells is performed to assess their energy yield potential under realistic illumination conditions with varying spectrum. We find that the yield of a 4-terminal contact scheme with thick top cell is more than 15% higher than for a 2-terminal scheme. Furthermore, we quantify the main losses that occur for this type of solar cell under varying spectra. Apart from current mismatch, we find that a significant power loss can be attributed to low irradiance seen by the sub-cells. The study shows that despite non-optimal bandgap combination, GaAs/Si tandem solar cells have the potential to surpass 30% energy conversion efficiency.

Detailed Current Loss Analysis for a PV Module Made With Textured Multicrystalline Silicon Wafer Solar Cells

We present a top-down method to quantify optical losses due to encapsulation of textured multicrystalline silicon wafer solar cells in a photovoltaic module. The approach is based on a combination of measurements and mathematical procedures. Seven different loss mechanisms are considered: 1) reflection at the glass front surface, 2) reflection at the metal fingers, 3) reflection at the textured solar cell surface, 4) absorption in the antireflection coating, 5) absorption in the glass pane and the encapsulation layer, 6) front surface escape, and 7) losses due to a non-perfect solar cell internal quantum efficiency. Losses for each of these mechanisms are obtained as a function of wavelength, and the corresponding current loss for each loss mechanism is calculated. Comparing simulated and measured results, the method predicts the module quantum efficiency with an error of less than 2% and the collected current with an error of less than 1%. In the presented example, the biggest loss (7.4 mA/cm 2) is due to the nonperfect quantum efficiency, followed by reflection losses at the glass front (2.2 mA/cm 2) and absorption in the glass and encapsulation layer (1.1 mA/cm 2).

Numerical Analysis of Radiative Recombination and Reabsorption in GaAs/Si Tandem

We demonstrate a numerical analysis of the device impact of photon reabsorption on single-junction GaAs and tandem GaAs/Si solar cells. A self-consistent optical-electrical model that considers nonideal losses within the devices is developed. For single-junction devices, we find that the impact of photon recycling on the voltage increases monotonically with the injection level. For record-level GaAs solar cells, the voltage boost is 33 mV under open-circuit conditions and 13 mV at the maximum power point. For tandem GaAs/Si solar cells, photon reabsorption moderates the sensitivity of tandem efficiency to both obvious parameters like absorber thickness and implicit parameters like shunt resistance (Rsh) and bulk lifetime. Considering luminescent coupling results in a GaAs top cell that is 9.5% thicker than without luminescent coupling. The tandem device is 50% more sensitive to Rsh changes in the GaAs cell than Rsh changes in the Si cell. The impact of the GaAs top-cell bulk lifetime on tandem efficiency is reduced by 61% if photon reabsorption is not considered. This integrated optoelectronic device model allows one quantification of the implicit effects of photon recycling and luminescent coupling on device parameters for GaAs/Si tandem, providing a valuable tool for high-performance device optimization.

Analysis of Fine-Line Screen and Stencil-Printed Metal Contacts for Silicon Wafer Solar Cells

Primary challenges to fine-line silver printing for solar cells are achieving high aspect ratios and uniform lines with a low level of striations. This paper compares two high-throughput printing technologies, namely, printing by screens versus stencils. A statistical method is introduced to evaluate the quality of the printed front grid based on the distributions of printed metal line profiles, line segment conductance, overall electroluminescence (EL) pattern, and solar cell light current-voltage (I-V) characteristics. The model distribution, combined with finite-element modeling to predict realistic cell-level voltage variations, adequately describes all four kinds of characteristics. It predicts well the diverging performance of screen- and stencil-printed solar cells as the line width becomes less than 50 μm. Experimentally, the highest batch average efficiency of 18.8% was achieved on 156 mm × 156 mm p-type monocrystalline silicon solar cells printed with stencils having 30-μm line openings, using only 78 mg of silver paste per cell.

Energy-yield prediction for II–VI-based thin-film tandem solar cells

Polycrystalline, thin-film tandem solar cells that leverage commercial II–VI semiconductor technologies as the top cell could overcome the practical conversion-efficiency limits of single-junction solar cells. However, it is unclear to what extent this class of tandems would outperform single-junction solar cells under realistic operating conditions in the field. In this paper we model the annual energy-yield of tandems with polycrystalline II–VI top cells with different band gap pairs and architectures under changing illumination spectra in different climates. We find that both two-terminal, high-band gap II–VI/CIGS and four-terminal CdTe/CIGS tandems offer energy-yield advantages in all climates commensurate with their AM1.5G efficiency improvements, up to [38%] relative. On the other hand, a two-terminal CdTe/GaSb tandem cell has only an [11%] annual energy-yield advantage in humid climate, because infrared light absorption due to atmospheric water vapor limits the bottom-cell contribution. In addition to narrowing the scope of future II–VI-based tandem R&D efforts, our methodology to rapidly assess tandem energy-yield should be easily generalizable to other material combinations.

Techno-economic analysis of tandem photovoltaic systems

Tandem solar cells offer the potential of conversion efficiencies exceeding those of single-junction solar cells, but also incur higher fabrication costs. The question arises under which conditions a tandem solar cell becomes economically preferable to both of the single-junction sub-cells it comprises. We present an analysis based on cost and efficiency relations to answer this question for a double-junction tandem solar cell. We find that combining two ideally band-gap-matched single-junction solar cell technologies into a tandem should be a “marriage of equals”: the sub cells should be produced at similar

A Quantitative Analysis of Photovoltaic Modules Using Halved Cells

per W costs, both sub cells should have similar efficiencies when operated independently, and the costs to turn both cells into a system should be similar. We discuss examples of different hypothetical and actual tandem solar cell technologies and show the intricacies of imbalances in the mentioned factors. We find that tandem-solar-cell-based PV power stations for existing solar-cell technologies offer the potential to reduce the levelized cost of electricity (LCOE), provided suitable top cells are developed.

Comparison of Glass/Glass and Glass/Backsheet PV Modules Using Bifacial Silicon Solar Cells

In a silicon wafer-based photovoltaic (PV) module, significant power is lost due to current transport through the ribbons interconnecting neighbour cells. Using halved cells in PV modules is an effective method to reduce the resistive power loss which has already been applied by some major PV manufacturers (Mitsubishi, BP Solar) in their commercial available PV modules. As a consequence, quantitative analysis of PV modules using halved cells is needed. In this paper we investigate theoretically and experimentally the difference between modules made with halved and full-size solar cells. Theoretically, we find an improvement in fill factor of 1.8% absolute and output power of 90 mW for the halved cell minimodule. Experimentally, we find an improvement in fill factor of 1.3% absolute and output power of 60 mW for the halved cell module. Also, we investigate theoretically how this effect confers to the case of large-size modules. It is found that the performance increment of halved cell PV modules is even higher for high-efficiency solar cells. After that, the resistive loss of large-size modules with different interconnection schemes is analysed. Finally, factors influencing the performance and cost of industrial halved cell PV modules are discussed.

The Impact of Haze on Performance Ratio and Short-Circuit Current of PV Systems in Singapore

Bifacial solar cells can be encapsulated in modules with either a glass/glass or a glass/backsheet structure. A glass/backsheet structure provides additional module current under standard test conditions (STC), due to the backsheet scattering effects, whereas a glass/glass structure has the potential to generate additional energy under outdoor conditions. In this study, we quantify the current contributions due to various mechanisms in both module structures under STC. The current contributions due to different mechanisms are calculated by measuring the reflectance and transmittance of mini-modules with both structures, together with a MATLAB-based simulation. Our results show that under STC, glass/backsheet modules provide approximately 2.2% more power, as compared with glass/glass modules using the same bifacial solar cells with a standard cell gap of 2.0 mm. Using module optimization, we demonstrate that the maximum possible cost reduction benefit in

An Empirical Model for Rack-Mounted PV Module Temperatures for Southeast Asian Locations Evaluated for Minute Time Scales

/WP of glass/backsheet modules over glass/glass modules under STC is limited to 3.3%. Due to the potential outdoor energy yield advantages of glass/glass modules reported in the literature, we recommend a glass/glass module structure for bifacial solar cells. Furthermore, in order to compensate for the lower performance of glass/glass modules under STC, we propose a methodology to measure and fairly rate bifacial glass/glass photovoltaic (PV) modules.