Si Thin Film Solar Cells Research Articles

Silicon nanohole based enhanced light absorbers for thin film solar cell applications

We proposed a nanohole-based silicon (Si) absorber structure to enhance the light absorption of thin-film Si solar cells. Our proposed structures exhibited excellent performances harnessing the light-matter interaction phenomenon with a few microns of thick Si (3 µm). We employed the finite-difference time-domain method to analyze the optical properties and solved Poisson’s, continuity, and heat transfer equations to analyze the electrical and thermal properties of our proposed structures, operating in the wavelength range from 300 to 1100 nm. We obtained a maximum average absorption of 72.6% for our proposed square hole Si absorber structure. The power conversion efficiency and short circuit current density were calculated to be 20.74% and 39.91 mA/cm2. We achieved polarization-insensitive performance due to the symmetrical nature of the structure. The temperature of our proposed structure was increased by ∼10 K due to light absorption for different ambient temperatures. Moreover, we found our proposed structure was thermally stable over time. Our proposed structures can enhance the absorption of Si nanostructures, which can be conducive to designing Si-thin solar cells for energy harvesting.

The Impact of P-Type Layer on Performance and Stability of Thin Film Silicon Solar Cells in Relation to Third Generation: A review Analysis

Thin-film Silicon (Si) Solar Cells (SCs) have emerged as a promising candidate for next-generation photovoltaic devices due to their potential for cost-effectiveness and versatility. However, achieving high efficiency and long-term stability remains a significant challenge in their development. The primary challenges with thin-film Si SCs have been the poor infrared light absorption of Hydrogenated Microcrystalline Silicon (c-Si: H) and the light-induced metastability of Hydrogenated Amorphous Silicon (a-Si: H). This study reviewed the influence of the p-type layer, a key component in thin-film Si SCs, on both performance and stability. Third generation SCs are optimized for high Power Conversion Efficiency (PCE) at low manufacturing costs. According to the review of the comparison analysis, Patel K. et al., (2021) obtained the highest PCE of 30.17% with the a-Si/MoTe2 material (Photocurrent Density Jsc = 32.41mA/cm2, An Open-Circuit Voltage Voc = 1.093V, and Fill Factor (FF) = 85.12%) of the state-of-the-art previous works. The findings presented here contribute valuable insights toward the development of efficient and durable SC technology, crucial for advancing the adoption of renewable energy sources in our ever-growing energy demand.

Thin film Si solar cell and solid oxide fuel cell technologies for a low cost, environmentally friendly and sustainable source of energy

Thin-film solar cell technology based on hydrogenated amorphous silicon has matured over the last two decades and is capable to deliver commercial modules with almost 10 % stabilized efficiency. Moreover attention on hydrogen fuel cells is increasing as the range of potential commercial applications expands, with more than 3800 fuel cell systems being installed and operated worldwide. These systems attain high theoretical efficiencies in the range of 43.7-70.4 %, with an additional 20% as heat recovery, and operating at carbon-free conditions between 50 °C and 900 °C. In this paper the status of thin-film silicon solar cell technology is reviewed by comparing it to other major solar cell technologies. A discussion is also made upon the benefits obtained from the few potential applications, as long-term potential actions for sustainable development, and the future of Solid Oxide Fuel Cells (SOFCs). Applications of thin-film silicon modules and SOFCs are presented. EPIA (European Photovoltaic Industry Association) estimates that half of the growth in the next two years will come from thin-film technology.

Enhanced Absorption in InP Nanodisk Arrays on Ultra-Thin-Film Silicon for Solar Cell Applications

The photovoltaic (PV) market today is dominated by silicon (Si)-based solar cells, which, however, can be improved in performance and cost by developing technologies that use less material. We propose an indium phosphide (InP) nanoresonator array on silicon ultra-thin film with a combined thickness of 0.5 μm to 2 μm as a solution to minimize cost and maximize power efficiency. This paper focuses on simultaneously achieving broadband antireflection and enhanced absorption in thin-film Si with integrated InP nanodisk arrays. Electromagnetic simulations are used to design and optimize the reflectance and absorption of the proposed design. By varying the height and radius of the InP nanodisks on the Si substrate, together with the array pitch, a weighted reflectance minimum, with respect to the AM1.5 solar spectrum, of 2.9% is obtained in the wavelength range of 400 nm to 1100 nm. The antireflective properties are found to be a combination of a Mie-resonance-induced strong forward-scattering into the structure and an effective index-matching to the Si substrate. In terms of absorption, even up to 2 μm from the Si surface the InP nanodisk/Si structure consistently shows superior performance compared to plain Si as well as a Si nanodisk/Si structure. At a depth of 500 nm from the surface of the substrate, the absorption values were found to be 47.5% for the InP nanodisk/Si structure compared to only 18.2% for a plain Si substrate. This shows that direct bandgap InP nanoresonator arrays on thin-film Si solar cells can be a novel design to enhance the absorption efficiency of the cell.

Design of a Highly Efficient Subwavelength Antireflective Structure for Solar Cells

An efficient optical antireflective (AR) structure plays a vital role in high-performance thin-film solar cells. Here, we design a surface relief AR structure consisting of a two-dimensional (2D) array of a subwavelength ring and pillar-shaped feature, capable of suppressing optical reflection over a wide spectral window of the solar spectrum. Our simulations show that the weighted average reflectance of the subwavelength AR structure is as low as 4.2% in the 400–1100 nm spectral range in the normal incidence condition and almost 10-fold reduction compared with a bare silicon surface. When placed on the front side of a simple Si thin-film photovoltaic solar cell, this subwavelength AR structure leads to an improved light absorption with simulated results showing an increase of 53% short-circuit current compared to a flat solar cell. Besides, our simulations show that this AR structure could, in principle, perform well against reasonable fabrication errors.

Crystallization of catalytic CVD hydrogenated n-a-Si films on textured glass substrates by flash lamp annealing

Flash lamp annealing (FLA) is a short-duration annealing technique that can crystallize amorphous silicon (a-Si) films for thin-film polycrystalline Si (poly-Si) solar cells. We investigated the crystallization of n-type hydrogenated a-Si (n-a-Si:H) films formed by catalytic chemical vapor deposition on Si nitride- (SiN x -) coated textured glass substrates. The n-a-Si:H films with a thickness of ∼2.7 μm were crystallized by FLA with no film peeling even without chromium adhesion layers. We also confirmed that the crystallization takes place through explosive crystallization (EC). The addition of phosphorous to the precursor a-Si:H slightly modifies the crystallization, resulting in different grain sizes and EC velocities compared to the case of EC of intrinsic a-Si:H.

The effect of different surface plasmon polariton shapes on thin-film solar cell efficiency

The effects of surface plasmon polaritons (SPPs) on the efficiency, series resistance, and shunt resistance of thin-film Si solar cells are studied and analyzed in this work. Different SPP shapes and their effects on the optical and electrical properties and thereby the efficiency of thin-film solar cells are studied. Semiconductor and electromagnetic models are incorporated to study the electrical and optical behaviors of the thin-film solar cells, respectively, using COMSOL Multiphysics three-dimensional (3D) numerical simulation software. An efficiency of 14.76% is achieved for triangular SPPs, representing a 1.07% improvement compared with SPP-free solar cells. The solar cell electrical parameters are also extracted based on a single-diode equivalent model. The series resistance is decreased by 3% for solar cells having equilateral-triangle SPPs compared with SPP-free solar cells.

Influence on the Haze Effect of Si Thin-Film Solar Cell on Multi-Surface Textures of Periodic Honeycomb Glass

Double textures were applied to use for multi-junction silicon thin film (Si-TF) solar cells. To improve the longer wavelength, we were formed the microscale periodic honeycomb textured surface on a glass substrate. We achieved the transmittance of 94.26% and found the approximately 52% for haze value. Etched AZO films on the textured glass is crucial role for improving the short-wavelength in Si-TF solar cells. Textured AZO film using a 1% HF solution is suitable for the growth of microcrystalline Si and better light trapping. The transmittance was recorded 80.8% that was 3% higher than that of reference fluorine doped tin oxide (FTO, Asahi-U type) glass. We also achieved for high haze value of 59.8% to enable the light trapping across the entire wavelength region. Using a finite-difference time-domain (FDTD) simulation, we designed a multi-junction Si-TF solar cells with high short-circuit current density of 12.5 mA/cm2. To reduce the plasma damage and surface stress on the μc-Si:H layer during growth, we fabricated an a-Si:H/µc-Si:H tandem cell on a multi-surface textures with a µc-Si:H layer of only 1.5 µm thick and obtained a conversion efficiency of 13.3%. The developed double textures structure and fabrication technique are expected to improve the performance of various multi-junction Si thin-film solar cells.

Versatility of Nanocrystalline Silicon Films: from Thin-Film to Perovskite/c-Si Tandem Solar Cell Applications

Doped hydrogenated nanocrystalline (nc-Si:H) and silicon oxide (nc-SiOx:H) materials grown by plasma-enhanced chemical vapor deposition have favourable optoelectronic properties originated from their two-phase structure. This unique combination of qualities, initially, led to the development of thin-film Si solar cells allowing the fabrication of multijunction devices by tailoring the material bandgap. Furthermore, nanocrystalline silicon films can offer a better carrier transport and field-effect passivation than amorphous Si layers could do, and this can improve the carrier selectivity in silicon heterojunction (SHJ) solar cells. The reduced parasitic absorption, due to the lower absorption coefficient of nc-SiOx:H films in the relevant spectral range, leads to potential gain in short circuit current. In this work, we report on development and applications of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) from material to device level. We address the potential benefits and the challenges for a successful integration in SHJ solar cells. Finally, we prove that nc-SiOx:H demonstrated clear advantages for maximizing the infrared response of c-Si bottom cells in combination with perovskite top cells.

Efficiency enhancement in Si solar cell using 1D quasi-periodic antireflection coating

In order to enhance the efficiency of thin-film Si solar cell, two well-known Fibonacci and Thue–Morse sequences of 1D quasi-periodic structures have been considered to achieve a broadband (300–1100 nm) planar antireflection coating, in this article. As almost non-absorbing materials in the solar spectrum, TiO2 and SiO2 with optimized thicknesses are considered to eliminate the reflections in the front side of the solar cell. An optimized bilayer antireflection coating with thicknesses of 54.4 nm and 85.6 nm respectively for the TiO2 and SiO2 layers has been obtained. Considering material dispersion and solar power spectrum (AM1.5), maximum efficiency enhancements of 42.78%, 46.15%, and 50% have been achieved for the 3 µm thin-film Si solar cell using the FC(3,1) structure which correspond to the cells without any recombination, with bulk recombination, and with bulk and surface recombinations, respectively. The proposed quasi-periodic multilayer antireflection structures have been investigated and optimized using the TMM and FDTD methods. The electrical characteristic of the design is studied by the drift–diffusion method after extracting the electron–hole pair generation. Also, the stability of the performance of the proposed ARC against induced roughness in practice has been investigated and discussed.

Investigation of quasi-periodic structures to increase the efficiency of thin-film silicon solar cells: A comparative study

To boost the energy conversion efficiency in a thin-film Si solar cell, the effect of applying simple and generalized Fibonacci and Thue-Morse quasi-periodic multilayers in the front and back sides have been investigated. The anti-reflection coating and the back reflector are composed of SiO2/TiO2 and SiO2/Si sequences, respectively and the obtained results are in a good agreement with previous studies. Also, a 2D square array photonic crystal with 12-fold basis has been introduced to enhance the optical path length and hence, the absorption probability for longer wavelengths due to excitation of higher-order diffraction modes. The study has been carried out using the transfer matrix method (TMM) and the finite difference time domain (FDTD) methods and the electrical characteristics have been obtained implementing the drift-diffusion. A reasonable enhancement of ~115% and more than 120% in the short circuit current density and conversion efficiency have been achieved, respectively in the optimized structure.

Narrow band gap high conducting nc-Si1-xGex:H absorber layers for tandem structure nc-Si solar cells

Advantages of spectral sensitivity in the infrared range and good stability against light exposure together have made nanocrystalline silicon–germanium alloy (nc-Si1-xGex) as an ideal absorber material at the bottom-cell in multi-junction Si thin film solar cells. Evolution of good quality SiGe thin films with sustained nanocrystallinity, particularly at low growth temperature (TS), is a challenging task in view of very different chemical reaction behaviors controlled via different energy requirements of two frequently used source gases, e.g., SiH4 and GeH4. Growth of nc-SiGe:H thin films have been pursued at TS ∼220 °C, using H2-diluted (by ∼96%) (SiH4 + GeH4) plasma in 13.56 MHz RF-PECVD, by varying the RF power applied to the parallel plate capacitively coupled electrodes of the reactor. At lower RF power Ge-dominated low band gap SiGe network has been produced with Si component in mostly amorphous configuration that leads to a low electrical conductivity. At high RF power Si–Si network becomes highly crystalline; however, Ge content reduces drastically. Breaking of weaker Ge–Ge bonds creates defects via dangling bonds and increased grain boundary defects around Si nanocrystals together produce relatively wider band gap SiGe network with degraded electrical conductivity. The novelty and significance of the present investigation remains in realizing the narrowing of the optical band gap (Eg ∼1.499 eV) even at lower Ge content, through moderate crystallization in the SiGe network and a simultaneous high electrical conductivity of the nc-SiGe:H films (σD ∼2.38 × 10−3 S cm−1) obtained at a high growth rate (∼9.5 nm/min), via optimization of the applied RF power at a moderate level (∼100 W). In such circumstances nanocrystallization of the network plays leading role in narrowing the optical band gap, overriding the effect arising out of the restricted presence of Ge.

Tailoring the Post-Etching of Room-Temperature-Fabricated H and Ti Co-Doped ZnO Films for Efficient Harvested Light Trapping

Chemical etching is widely applied to texture the surface of sputter-deposited zinc oxide films for efficient light-scattering in silicon thin-film solar cells. Based on experimental findings from our previous studies, two types of experimental techniques, a combination of HCl/NaOH and NaOH/HCl etching modes as well as a multi-step etching process, were considered to improve the light-trapping ability of room-temperature-deposited H and Ti co-doped ZnO (HTZO) films. The effects of the employed experimental procedures on the optical, electrical, and morphological properties of the HTZO films were systematically investigated. After optimization, higher haze values of 96.2%, 90.6%, and 74% at 550 nm, 800 nm, and 1100 nm, as well as a higher average haze value of 90.1% in the range of 400–1100 nm were achieved, which are better than those of the reference conventional HCl-etched Al-doped ZnO (AZO), high-light-trapping AZO, and SnO2:F films. These findings reveal a method to develop high-performance ZnO films for the front electrodes in high-efficiency Si thin-film solar cells.

Replacement of n-type layers with a non-toxic APTES interfacial layer to improve the performance of amorphous Si thin-film solar cells.

Hydrogenated amorphous Si (a-Si:H) thin-film solar cells (TFSCs) generally contain p/n-type Si layers, which are fabricated using toxic gases. The substitution of these p/n-type layers with non-toxic materials while improving the device performance is a major challenge in the field of TFSCs. Herein, we report the fabrication of a-Si:H TFSCs with the n-type Si layer replaced with a self-assembled monolayer (3-aminopropyl) triethoxysilane (APTES). The X-ray photoelectron spectroscopy results showed that the amine groups from APTES attached with the hydroxyl groups (–OH) on the intrinsic Si (i-Si) surface to form a positive interfacial dipole towards i-Si. This interfacial dipole facilitated the decrease in electron extraction barrier by lowering the work function of the cathode. Consequently, the TFSC with APTES showed a higher fill factor (0.61) and power conversion efficiency (7.68%) than the reference device (without APTES). This performance enhancement of the TFSC with APTES can be attributed to its superior built-in potential and the reduction in the Schottky barrier of the cathode. In addition, the TFSCs with APTES showed lower leakage currents under dark conditions, and hence better charge separation and stability than the reference device. This indicates that APTES is a potential alternative to n-type Si layers, and hence can be used for the fabrication of non-toxic air-stable a-Si:H TFSCs with enhanced performance.

Enhancement of light trapping for thin film solar cells

ABSTRACTLight trapping is one of the key challenges for next generation thin film solar cells. In this work, we have identified the distinct light trapping effects for short and long wavelength solar spectrum range, by investigating lighting trapping structures on both sides of Si thin film solar cells. The sub-wavelength photonic front surface by wet etching and multi-layer photonic crystal reflector on the bottom surface are studied in detail for its solar energy absorption characteristics. Our study reveals the drastic difference of the light trapping effects within the solar spectrum wavelength. This work may provide guidance for the efficiency enhancementfor next generation thin film photovoltaic cells.

High-efficiency heterojunction crystalline Si solar cells

High-efficiency back-contact heterojunction crystalline Si (c-Si) solar cells with record-breaking conversion efficiencies of 26.7% for cells and 24.5% for modules are reported. The importance of thin-film Si solar cell technology for heterojunction c-Si solar cells with amorphous Si passivation layers in improving conversion efficiency and reducing production cost is demonstrated. Our attempts to reduce the production cost of a heterojunction c-Si solar cell by applying a SiOx layer prepared by a plasma-enhanced CVD method are presented. The characteristics of heterojunction c-Si solar cells are clarified by comparing them with those of practical homojunction solar cells, and crucial targets for industrialization of back-contact heterojunction c-Si solar cells are discussed. Owing to the recent improvement of c-Si solar cells and perovskite solar cells, conversion efficiencies over 30% have become a realistic target by using a two-terminal tandem structure with a heterojunction c-Si solar cell and a perovskite solar cell.

Colored and semitransparent silver nanoparticle layers deposited by spin coating of silver nanoink

In this letter, we report on the fabrication and characterization of colored and semitransparent silver nanoparticle layers. A spin coating of silver nanoink is used to deposit silver nanoparticle layers onto substrates. The transmittance and color of the silver nanoparticle layers are significantly dependent on the spin speed and nanoink concentration, owing to variations in the size and distribution of the nanoparticles. Both color variation and efficiency improvement are achieved with the application of silver nanoparticles to semitransparent Si thin-film solar cells, which is associated with the excitation of the dipole or quadruple plasmon modes of the silver nanoparticles.

Rear texturing for light-trapping in laser-crystallised silicon thin-film solar cells on glass

This paper presents optimisation of rear Si texturing by KOH-based solution for enhanced light-trapping in liquid-phase crystallised Si thin-film solar cells on glass. Texturing with 3 µm Si removal exhibits the largest absorption enhancement (compared with 1 and 2 µm Si removal) due to the enhanced light scattering by the rear pyramidal features. In the solar cells with SiOx/SiNx/SiOx buffer layer (with anti-reflection effect), the Jsc is found to increase from 20.4 (planar reference) to 22.6 mA/cm2 (10.8% enhancement) with the optimised rear Si texturing. The Voc and pFF are not degraded. After incorporating white paint back surface reflector and front anti-reflection foil to the rear-textured solar cells, Jsc up to 25.4 mA/cm2 (24.5% relative enhancement) is achieved.

Light trapping mechanism of hemisphere cone arrays for silicon solar cells

Hemisphere cone arrays (HCAs) is a popular light trapping structure in silicon solar cells. However, the light trapping mechanism research of that in solar cells is lacking. In this paper, the light trapping mechanism of the HCAs in silicon solar cells is studied by combination of numerical analysis and geometrical optics simulation. The results show that the HCAs structure can reduce surface reflectance by ∼60% compared with flat structure by multiple injections of the incident light. At the same time, the HCAs can make ∼43% unabsorbed light return to the absorbing layer of solar cells again. To verify the theoretical calculation results, a flat and a square hemispherical cone arrays PDMS thin films are prepared by a micro/nano-processing method, and the reflectivities of a silicon wafer covered the flat and the HCAs PDMS thin films were measured. The experimental measured results are basically consistent with the theoretical calculation results. The numerical calculation results also show that the total optical path length of the thin film Si solar cell covered with the HCAs structure increases from 2ω to 4ω.

Low-Temperature Growth of Hydrogenated Amorphous Silicon Carbide Solar Cell by Inductively Coupled Plasma Deposition Toward High Conversion Efficiency in Indoor Lighting

A p-a-SiC:H window layer was used in amorphous Si thin film solar cells to boost the conversion efficiency in an indoor lighting of 500 lx. The p-a-SiC:H window layer/p-a-Si:H buffer layer scheme moderates the abrupt band bending across the p/i interface for the enhancement of VOC, JSC and FF in the solar spectra of short wavelengths. The optimized thickness of i-a-Si:H absorber layer is 400 nm to achieve the conversion efficiency of ~9.58% in an AM1.5 G solar spectrum. However, the optimized thickness of the absorber layer can be changed from 400 to 600 nm in the indoor lighting of 500 lx, exhibiting the maximum output power of 25.56 μW/cm2. Furthermore, various durability tests with excellent performance were investigated, which are significantly beneficial to harvest the indoor lights for applications in the self-powered internet of thing (IoT).