Lei Hong

High efficiency silicon nanohole/organic heterojunction hybrid solar cell

High efficiency hybrid solar cells are fabricated based on silicon with a nanohole (SiNH) structure and poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The SiNH structure is fabricated using electroless chemical etching with silver catalyst, and the heterojunction is formed by spin coating of PEDOT on the SiNH. The hybrid cells are optimized by varying the hole depth, and a maximum power conversion efficiency of 8.3% is achieved with a hole depth of 1u2009μm. The SiNH hybrid solar cell exhibits a strong antireflection and light trapping property attributed to the sub-wavelength dimension of the SiNH structure.

Design guideline of Si nanohole/PEDOT:PSS hybrid structure for solar cell application

The finite element method is used to simulate light absorption in periodic hybrid Si nanohole (SiNH)/PEDOT:PSS arrays. The structural periodicity (P) and hole diameter (D) of the hybrid SiNH structure are varied to maximize light absorption. In terms of the solar cell performance under the AM1.5G spectrum, the highest ultimate efficiency achieved is 30.5%, when the D/P ratio is 0.8 and P is 600xa0nm. We have successfully fabricated the SiNH structure based on a low cost electroless chemical etching approach using a silver catalyst. The SiNH diameters formed vary from ∼200 to 300xa0nm, with periodicities from ∼300 to 1000xa0nm. The SiNH structure reveals a low average reflectance of 4% for incident light in the range 300 to 1100xa0nm.

Design guidelines for slanting silicon nanowire arrays for solar cell application

The reflectance and absorption characteristics of slanting silicon nanowires (SiNWs) structure have been simulated using finite element method to provide a design guideline for its application in solar cell. The slanting angle for the nanowire structure is set at 40° on Si (111) wafer. The impact of the structural periodicity (P) and wire diameter/periodicity (D/P) ratio on the optical characteristics of the slanting SiNW has been systematically analyzed. It has been found that due to the much suppressed light reflection and stronger light trapping ability, the light absorption is significantly enhanced for the slanting SiNW structure compared with vertical SiNW structure. The optimal absorption condition is achieved when Pu2009=u2009800u2009nm and D/Pu2009=u20090.7, yielding the highest ultimate efficiency of 33.45%. The result is better than the 28.36% that can be achieved for optimum vertical SiNWs. A comparison of the absorption characteristics of optimum slanting and vertical SiNWs structures is presented and analyzed i...

Design principles for plasmonic thin film GaAs solar cells with high absorption enhancement

In this paper, a systematic design and analysis of gallium arsenide thin film solar cells incorporated with a periodic silver nanoparticles (NPs) structure to enhance light absorption is presented using the finite element method. The influence of the silver nanoparticles diameter and structure periodicity on light absorption has been examined. It is found that the absorption is significantly enhanced due to the surface plasmon induced by the silver nanoparticles. The optimal structural parameters are achieved when the diameter of the nanoparticles is 200u2009nm and the periodicity is 444u2009nm. This gives rise to a maximum ultimate photocurrent of 26.32 mA/cm2 under AM1.5G solar irradiation. In addition, the underlying physics that accounts for the enhancement is discussed.In this paper, a systematic design and analysis of gallium arsenide thin film solar cells incorporated with a periodic silver nanoparticles (NPs) structure to enhance light absorption is presented using the finite element method. The influence of the silver nanoparticles diameter and structure periodicity on light absorption has been examined. It is found that the absorption is significantly enhanced due to the surface plasmon induced by the silver nanoparticles. The optimal structural parameters are achieved when the diameter of the nanoparticles is 200u2009nm and the periodicity is 444u2009nm. This gives rise to a maximum ultimate photocurrent of 26.32 mA/cm2 under AM1.5G solar irradiation. In addition, the underlying physics that accounts for the enhancement is discussed.

Crystallization and surface texturing of amorphous-Si induced by UV laser for photovoltaic application

The DPSS Nd:YVO4 UV laser is used to anneal amorphous silicon (a-Si) film to achieve crystallization and nano-dome surface texturing simultaneously in a one-step annealing process. With pulse energy of 380 mJ/cm2 and repetition rate of 20 kHz, the a-Si can be crystallized by the sequential lateral solidification process, which is evidenced by both SEM characterization and Raman spectra. In addition, the nano-dome like structure is confirmed by AFM characterization, which can lead to ∼200% boost in terms of light absorption as measured by UV-Visible - Near-infrared scanning spectrophotometer. This study highlights the great potential of Nd:YVO4 UV laser for its application in thin film Si solar cell industry to improve the film quality and light trapping capability.

Light trapping in hybrid nanopyramid and nanohole structure silicon solar cell beyond the Lambertian limit

We propose a hybrid nanostructure that comprises nanopyramids and nanoholes for thin film silicon (Si) solar cells. The hybrid structure demonstrates a stronger light trapping ability that is beyond the Lambertian limit. This is achieved with the smaller dimension nanohole structure which effectively reduces shorter wavelength light reflection, and the larger dimension nanopyramid structure which significantly enhances longer wavelength light trapping. An ultimate efficiency of 38.3% is yielded for a 2u2009μm thick Si cell incorporated with the hybrid structure, which is higher than that achievable corresponding to the Lambertian limit. Moreover, the high ultimate efficiency is retained as the incident angle increases from normal incidence to 50° for TM polarized sunlight. Therefore, the proposed hybrid structure is very promising to enhance the performance of thin film Si solar cells.

Simulated optical absorption enhancement in random silicon nanohole structure for solar cell application

We have conducted a systematic simulation study on light absorption in a silicon nanohole structure that has randomness introduced into its structural parameters, which include the hole radius, depth, and position. It is found that light absorption is enhanced for the random structures compared to their periodic counterparts. This is attributed to additional resonances induced by the structural disorders, broadening of the existing resonance, and lower optical reflection. The highest light absorption is obtained for the structure with randomness in hole position, which achieves a 12.7% enhancement compared with the periodic structure.

Design Guidelines for Si(1 1 1) Inclined Nanohole Arrays in Thin-Film Solar Cells

In this paper, the slanting silicon nanohole (SiNH) structure is systematically designed and analyzed by simulation using the finite-element method. The slanting angle of the SiNH structure is fixed at 40° based on the Si(111) wafer. The impact of the SiNH diameter (D) and structural periodicity (P) on the light absorption has been examined. It is found that the absorption is significantly enhanced due to the much suppressed light reflection on the top surface and the strong light trapping ability of the slanting SiNH structure. At the P of 700 nm and D/ P ratio of 0.85, the optimal structural parameters are achieved with the highest ultimate efficiency of 32.9%. It is higher than that of the vertical SiNH structure counterpart which has a value of 29.7%. The physical mechanism of the enhanced light absorption is also discussed.

Femtosecond laser induced nanocone structure and simultaneous crystallization of 1.6 µm amorphous silicon thin film for photovoltaic application

In this paper, we have demonstrated the crystallization and simultaneous formation of the nanocone structure on the 1.6 µm thick amorphous silicon (a-Si) film using a one-step femtosecond laser annealing approach. The a-Si layer is crystallized after the annealing process, as confirmed from their Raman spectra. Meanwhile, the conical structures with diameters ranging from 160 nm to 1.4 µm are formed upon laser beam irradiation at different fluences, as deduced from scanning electron microscope and atomic force microscope characterization. The highest absorption is achieved when the sample is irradiated with a laser fluence of 588 mJ cm−2. The developed process has potential applications in the fabrication of high efficiency and low cost Si thin-film solar cells. Moreover, the physics and mechanism involved in the laser annealing process are also discussed.

Design guidelines for (111) Si inclined nanohole arrays in thin film solar cells

In this paper, a systematic design and analysis of slanting silicon nanohole structure is simulated using the finite element method. The slanting nanohole structure is based on the Si (111) wafer. The impact of the hole diameter and structural periodicity has been investigated. It is found that the absorption is significantly enhanced due to the strong light trapping ability of slanting nanohole structure. The optimal structural parameters are achieved when the periodicity is 700 nm and the diameter to periodicity ratio is 0.85. The highest ultimate efficiency achieved is 32.9%, higher than that of vertical nanohole structure with a value of 29.7%.