Performance Of Ultra-thin Solar Cells Research Articles

Optical absorption enhancement in ultrathin chalcopyrite solar cells with Ag reflective back contact

The optical performance of ultrathin solar cells based on chalcopyrite CuInS2 absorber has been studied, simulating the total absorption as a function of the absorber thickness with and without Ag reflective back contact. The structure chosen is ZnO:Al/SnS2/CuInS2/Ag/Mo/glass, using for the simulation the experimental data extracted from the layers prepared in our laboratory by evaporation (CuInS2 and SnS2) and sputtering (ZnO:Al, Ag and Mo). The main purpose has been to apply realistic input parameters (refractive index and extinction coefficient extracted from transmittance and reflectance measurements for each layer) to simulate and analyze the optical behavior of the entire device. It is found that the overall absorption of the cell with 0.2 μm-thick CuInS2 and 60 nm-thick Ag is the same as that obtained for 0.4 μm-thick CuInS2 without Ag layer. Thus, the incorporation of Ag reflective contact allows reducing the absorber layer thickness and therefore the time and cost of manufacturing chalcopyrite cells, being especially relevant for absorber thicknesses below 0.4 μm.

3‐D Modeling of Ultrathin Solar Cells with Nanostructured Dielectric Passivation: Case Study of Chalcogenide Solar Cells (Adv. Theory Simul. 11/2021)

3-D Modeling of Ultrathin Solar Cells In article number 2100191, Waseem Raja, Erkan Aydin, Thomas G. Allen, and Stefaan De Wolf develop a novel 3-D optoelectrical finite-element model to analyze the performance of ultrathin solar cells. In particular, the 3-D model investigates the light trapping and field passivation in which the negative charges induced on the nanostructured passivation layer repel the minority charge carriers, increasing the solar cell's open-circuit voltage and power conversion efficiency.

Light absorption enhancement in ultrathin perovskite solar cells using light scattering of high-index dielectric nanospheres.

Arrays of high-index dielectric nanoparticles supporting both electrical and magnetic resonances have gained increasing attention for their excellent light-trapping (LT) effects, thus greatly improving the performance of ultrathin solar cells. This work explores front-located, high-index dielectric subwavelength nanosphere arrays as an efficient and broadband LT structure patterned on top of an ultrathin perovskite solar cell (PSC) for a greatly enhanced absorption. Combined strong light scattering and anti-reflection properties achieved by optimized geometrical parameters of the LT structure lead to a broadband absorption enhancement in the ultrathin thickness of a photoactive layer (100 nm) yielding the short-circuit current density (Jsc) of 18.7 mA/cm2, which is 31.7% higher than that of a planar counterpart. Moreover, effects of the LT structure on far-field radiation patterns, scattering cross-sections, multipoles' contributions, and asymmetry parameters along with the incidence angle and polarization dependence are investigated. The present strategy could be applied to diverse applications, such as other ultrathin or semitransparent solar cells, absorbers and photodetectors.

3‐D Modeling of Ultrathin Solar Cells with Nanostructured Dielectric Passivation: Case Study of Chalcogenide Solar Cells

AbstractUltrathin solar cells can be a path forward to low‐cost photovoltaics due to their reduced material consumption and shorter required deposition times. With excellent surface passivation, such devices may feature higher open‐circuit voltages (VOC). However, their short‐circuit current density (JSC) may be reduced due to decreased light absorption. This mandates implementation of efficient light‐trapping structures. To design efficient ultrathin solar cells that combine surface‐passivation and light‐trapping features, accurate 3‐D modeling is necessary. To this end, a novel 3‐D optoelectrical finite‐element model is developed to analyze the performance of ultrathin solar cells. The model is applied to the case of ultrathin (<500 nm) chalcogenide solar cells (copper indium gallium (di) selenide, CIGSe), rear‐passivated with nanostructured Al2O3 to circumvent optical and electrical losses. It is found that such a nanopatterned dielectric passivation scheme enhances broadband light‐trapping with reduced rear‐surface recombination, resulting in an absolute power conversion efficiency enhancement of 3.9%, compared to cells without passivation structure. Overall, the work shows how 3‐D finite element modeling can aid in analyzing and developing new optical and electrical solar cell designs for ultrathin solar cells such as those based on chalcogenides and perovskites.

Design of high performance and low resistive loss graphene solar cells

Despite metallic plasmonic excitations can enhance the performance of ultra-thin solar cells however these so-called plasmonic solar cells suffer from a large resistive (Ohmic) loss caused by metallic elements. In this work, we report on a new design that uses graphene nanoribbons (GNRs) in a two-dimensional (2D) grating form at the top of the semiconductor-on-insulator (SOI) solar cells aimed to reduce the resistive loss. The results showed that GNRs can remarkably reduce the resistive loss compared to the SOI cell with Ag nanograting, while keeping all other cell’s parameters, comparable with those of Ag SOI cell. Optical absorption and short-circuit current density of the graphene cells showed, respectively, enhancements of 18 and 1.7 times when optimizations were done with respect to width and the grating period. Our calculations showed that the graphene solar cells dissipate at most 5% of incident sunlight power as narrow and tiny peaks around 508 nm, which is noticeably lower than those of Ag solar cells with high and broad band peaks with the maximum values of 29% at 480 nm and 24% at 637 nm.

Geometrical optimisation of core-shell nanowire arrays for enhanced absorption in thin crystalline silicon heterojunction solar cells.

Background: Elongated nanostructures, such as nanowires, have attracted significant attention for application in silicon-based solar cells. The high aspect ratio and characteristic radial junction configuration can lead to higher device performance, by increasing light absorption and, at the same time, improving the collection efficiency of photo-generated charge carriers. This work investigates the performance of ultra-thin solar cells characterised by nanowire arrays on a crystalline silicon bulk.Results: Proof-of-concept devices on a p-type mono-crystalline silicon wafer were manufactured and compared to flat references, showing improved absorption of light, while the final 11.8% (best-device) efficiency was hindered by sub-optimal passivation of the nanowire array. A modelling analysis of the optical performance of the proposed solar cell architecture was also carried out. Results showed that nanowires act as resonators, amplifying interference resonances and exciting additional wave-guided modes. The optimisation of the array geometrical dimensions highlighted a strong dependence of absorption on the nanowire cross section, a weaker effect of the nanowire height and good resilience for angles of incidence of light up to 60°.Conclusion: The presence of a nanowire array increases the optical performance of ultra-thin crystalline silicon solar cells in a wide range of illumination conditions, by exciting resonances inside the absorber layer. However, passivation of nanowires is critical to further improve the efficiency of such devices.

Circuit Modeling of Waveguide Grating Nanostructures in Ultrathin Solar Cells

In this paper, a circuit modeling is used to investigate the effects of waveguide grating nanostructures on the performance of ultrathin solar cells. The proposed method is based on transmission line equivalent circuit (TLEC) and it is identified for both of the transverse electric and transverse magnetic polarizations. Under assumption of weak-coupling condition, this method can effectively describe the absorption inside ultrathin solar cells with the one-dimensional grating nanostructure etched into the anti-reflection coating layers. The proposed approach consists of two different circuits accounting for the background and scattering fields. The final result of the TLEC method comprises of the superposition of the background and scattering TLEC circuits.

Optimization of periodic nanostructures for enhanced light-trapping in ultra-thin photovoltaics

Nanophotonic light trapping offers a promising approach to increased efficiency in thin-film organic photovoltaics. In this paper, an extension of the direct-binary-search algorithm was adopted to optimize dielectric nanophotonic structures for increasing power output of ultra-thin organic solar cells. The optimized devices were comprised of an absorber layer sandwiched between two patterned, transparent, conducting cladding layers. Light trapping in such devices with an absorber thickness of only 10nm increases power output by a factor of 16 when compared to a flat reference device. We further show that even under oblique illumination with angles ranging from 0 to 60 degrees, such a device could produce over 7 times more power compared to a flat reference device. Finally, we also performed a spectral and parametric analysis of the optimized design, and show that the increase is primarily due to guided-mode resonances. Our simulations indicate that this new design approach has the potential to significantly increase the performance of ultra-thin solar cells in realistic scenarios.