Boyuan Cai

Broadband Enhancement in Thin-Film Amorphous Silicon Solar Cells Enabled by Nucleated Silver Nanoparticles

Recently plasmonic effects have gained tremendous interest in solar cell research because they are deemed to be able to dramatically boost the efficiency of thin-film solar cells. However, despite of the intensive efforts, the desired broadband enhancement, which is critical for real device performance improvement, has yet been achieved with simple fabrication and integration methods appreciated by the solar industry. We propose in this paper a novel idea of using nucleated silver nanoparticles to effectively scatter light in a broadband wavelength range to realize pronounced absorption enhancement in the silicon absorbing layer. Since it does not require critical patterning, experimentally these tailored nanoparticles were achieved by the simple, low-cost and upscalable wet chemical synthesis method and integrated before the back contact layer of the amorphous silicon thin-film solar cells. The solar cells incorporated with 200 nm nucleated silver nanoparticles at 10% coverage density clearly demonstrate a broadband absorption enhancement and significant superior performance including a 14.3% enhancement in the short-circuit photocurrent density and a 23% enhancement in the energy conversion efficiency, compared with the randomly textured reference cells without nanoparticles. Among the measured plasmonic solar cells the highest efficiency achieved was 8.1%. The significant enhancement is mainly attributed to the broadband light scattering arising from the integration of the tailored nucleated silver nanoparticles.

Near-field light concentration of ultra-small metallic nanoparticles for absorption enhancement in a-Si solar cells

Near-field light concentration from plasmonic nanostructures was predicted to significantly improve solar cell conversion efficiency since the inception of plasmonic solar cells. However the challenge remains in designing effective nanostructures for useful near-field enhancement much exceeding the detrimental ohmic loss and light blockage losses in solar cells. We propose and demonstrate ultra-small (a few nanometers) gold nanoparticles integrated in amorphous silicon solar cells between the front electrode and the photoactive layer. Significant enhancements in both the photocurrent (14.1%) and fill factor (12.3%) have been achieved due to the strong plasmonic near-field concentration and the reduced contact resistance, respectively.

4-fold photocurrent enhancement in ultrathin nanoplasmonic perovskite solar cells.

Although perovskite materials have been widely investigated for thin-film photovoltaic devices due to the potential for high efficiency, their high toxicity has pressed the development of a solar cell structure of an ultra-thin absorber layer. But insufficient light absorption could be a result of ultra-thin perovskite films. In this paper, we propose a new nanoplasmonic solar cell that integrates metal nanoparticles at its rear/front surfaces of the perovskite layer. Plasmon-enhanced light scattering and near-field enhancement effects from lumpy sliver nanoparticles result in the photocurrent enhancement for a 50 nm thick absorber, which is higher than that for a 300 nm thick flat perovskite solar cell. We also predict the 4-fold photocurrent enhancement in an ultrathin perovskite solar cell with the absorber thickness of 10 nm. Our results pave a new way for ultrathin high-efficiency solar cells with either a lead-based or a lead-free perovskite absorption layer.

Graphenized Carbon Nanofiber: A Novel Light‐Trapping and Conductive Material to Achieve an Efficiency Breakthrough in Silicon Solar Cells

An innovative 1D material--graphenized carbon nanofiber--is designed and synthesized. The nanofiber exhibits superior light-scattering properties, ultralow absorption loss, and high electrical conductivity, and enables a wide range of applications. Simply integrating the nanofibers with the state-of-the-art silicon solar cells leads to a leaping efficiency boost of 3.8%, almost five times higher than the current world record.

Efficiently-cooled plasmonic amorphous silicon solar cells integrated with a nano-coated heat-pipe plate

Solar photovoltaics (PV) are emerging as a major alternative energy source. The cost of PV electricity depends on the efficiency of conversion of light to electricity. Despite of steady growth in the efficiency for several decades, little has been achieved to reduce the impact of real-world operating temperatures on this efficiency. Here we demonstrate a highly efficient cooling solution to the recently emerging high performance plasmonic solar cell technology by integrating an advanced nano-coated heat-pipe plate. This thermal cooling technology, efficient for both summer and winter time, demonstrates the heat transportation capability up to ten times higher than those of the metal plate and the conventional wickless heat-pipe plates. The reduction in temperature rise of the plasmonic solar cells operating under one sun condition can be as high as 46%, leading to an approximate 56% recovery in efficiency, which dramatically increases the energy yield of the plasmonic solar cells. This newly-developed, thermally-managed plasmonic solar cell device significantly extends the application scope of PV for highly efficient solar energy conversion.

Hetero-structured lumpy nanoparticle conformal structure for high absorbance of ultrathin film amorphous silicon solar cells

We present a concept for enhancing the absorbance of amorphous-silicon solar cells by using hetero-structured nanoparticles consisting of dielectric core particles combined with small metallic surface nanoparticles half embedded in the core to harness both the scattering effect and the near field light concentration. Through optimising key parameters, including the relative distance of the nanoparticles to the solar cell, the radius ratio of the core to the surface nanoparticles, and the refractive index of the core particles, the short circuit current density in a 20 nm nanoparticle-integrated active layer is equivalent to that in a 300 nm flat active layer.

Ultraviolet Plasmonic Aluminium Nanoparticles for Highly Efficient Light Incoupling on Silicon Solar Cells

Plasmonic metal nanoparticles supporting localized surface plasmon resonances have attracted a great deal of interest in boosting the light absorption in solar cells. Among the various plasmonic materials, the aluminium nanoparticles recently have become a rising star due to their unique ultraviolet plasmonic resonances, low cost, earth-abundance and high compatibility with the complementary metal-oxide semiconductor (CMOS) manufacturing process. Here, we report some key factors that determine the light incoupling of aluminium nanoparticles located on the front side of silicon solar cells. We first numerically study the scattering and absorption properties of the aluminium nanoparticles and the influence of the nanoparticle shape, size, surface coverage and the spacing layer on the light incoupling using the finite difference time domain method. Then, we experimentally integrate 100-nm aluminium nanoparticles on the front side of silicon solar cells with varying silicon nitride thicknesses. This study provides the fundamental insights for designing aluminium nanoparticle-based light trapping on solar cells.

Entire band absorption enhancement in double-side textured ultrathin solar cells by nanoparticle imprinting

Entire band light management is crucial for amorphous silicon (a-Si) solar cells, especially when the absorbing layer becomes ultrathin. Here, we propose and demonstrate a double-side texture strategy to effectively manage light in ultrathin solar cells via a simple and scalable nanoparticle imprinting technique. SiO2 nanoparticles are half embedded into the top surface of the solar cells to introduce the double-side texture. Using a solar cell with a 150 nm thick a-Si layer as an example, we observe significant enhancement over the entire absorption band of a-Si both theoretically and experimentally. A maximum short circuit current density enhancement as high as 43.9% has been achieved experimentally compared with a flat solar cell.

Significant light absorption enhancement in silicon thin film tandem solar cells with metallic nanoparticles.

Enhancing the light absorption in microcrystalline silicon bottom cell of a silicon-based tandem solar cell for photocurrent matching holds the key to achieving the overall solar cell performance breakthroughs. Here, we present a concept for significantly improving the absorption of both subcells simultaneously by simply applying tailored metallic nanoparticles both on the top and at the rear surfaces of the solar cells. Significant light absorption enhancement as large as 56% has been achieved in the bottom subcells. More importantly the thickness of the microcrystalline layer can be reduced by 57% without compromising the optical performance of the tandem solar cell, providing a cost-effective strategy for high performance tandem solar cells.

Plasmonic Nanovoid Combined with Front Side Partially Embedded SiO2 Nanoparticles for Whole Spectrum Enhanced a-silicon Solar Cells

Nanovoid structures are induced into a-Si solar cell by partially embedded nanoparticles inside the device from the top surface. Whole spectrum absorption enhancement is achieved with a measured short circuit current density enhancement of 30%.