Single Crystalline Silicon Solar Cells Research Articles

Perovskite/silicon tandem solar cells-compositions for improved stability and power conversion efficiency.

Perovskite/Silicon Tandem Solar Cells (PSTSCs) represent an emerging opportunity to compete with industry-standard single junction crystalline silicon (c-Si) solar cells. The maximum power conversion efficiency (PCE) of single junction cells is set by the Shockley-Queisser (SQ) limit (33.7%). However, tandem cells can expand this value to ~ 45% by utilising two stacked solar cells to harvest the solar spectrum more efficiently. 33.9% PCE has already been achieved with PSTSCs. This perspective analyses recent advances in PSTSC technology, with an emphasis on optimal perovskite composition, the problem and mitigation of light-induced halide phase segregation, self-assembled hole transporting monolayers and additives that can improve and stabilise the perovskite. Top-performing compositions show three cationic components (Cs+, FA+, Pb2+) and three anionic (I-, Br-, Cl-) with a bandgap between 1.55 and 1.77eV and a theoretical maximum of 1.73eV (717nm). Anionic additives such as (Br3)- and SCN- reduce trap states and segregation. 2D-perovskite grain boundary interfaces are created with cationic alkylammonium additives such as methyl-phenethylammonium (MPEA) and result in improved performance. 2-, 3- or 4-terminal devices with a (partly) textured silicon heterojunction (SHJ) bottom cell are ideal. An ultra-thin interfacial recombination layer (~ 5nm) of indium tin oxide (ITO) or indium zinc oxide (IZO) containing a carbazole-based hole transporting self-assembled monolayer (Me-4PACz) is used for optimal 2-terminal tandem devices.

Pulsed laser deposition of ZnO and MoO3 as reflection prohibitors on photovoltaic cell substrate to enhance the efficiency

With the ever-growing demand for conventional fuels, the improvement in the efficiency of the photovoltaic system is the need of the hour. Antireflection coatings enhance the availability of solar power by reducing the percentage of light reflected. A new coating has been developed to improve the solar cell's overall efficiency. This study focuses on enhancing the efficiency of the monocrystalline solar cell when a coating of ZnO-MoO3 is applied at a certain thickness. A layer of ZnO followed by MoO3 is deposited on a Silicon solar cell substrate using a Pulsed Laser Deposition process. Due to the transmissivity d between the two materials, they act as excellent antireflection coating. The layer thickness has been engineered to lie in the maximum absorption spectrum of monocrystalline silicon solar cells, which is between 400 and 800 nanometers. Based on the calculation of transmissivities for a given layer thickness of coating material, the coating has been done, and the efficiencies of the coated specimen were compared with the uncoated solar cell. The percentage improvement in the electrical efficiency of a single crystalline silicon solar cell with an anti-reflection coating at 1059 W/m2 is about 35.7%. Among the available antireflection coating materials, the combination that provides better efficiency when coated on top of a solar cell is hard to find. This anti-reflection coating could be a better solution to enhance the overall efficiency of the single crystalline silicon solar cell. Although ZnO and MoO3 coatings have been investigated separately for improvement in solar cell efficiency with varying levels of success, the hybrid coating of ZnO/MoO3 with a performance enhancement of 35.7% is a great leap.

Flexible and Semi-Transparent Silicon Solar Cells as a Power Supply to Smart Contact Lenses.

Supplying electric power to wearable IoT devices, particularly smart contact lenses (SCLs), is one of the main obstacles to widespread adoption and commercialization. In the present study, we have successfully designed, fabricated, and characterized semi-transparent, self-supported, and flexible single crystalline silicon solar cells using a single-sided micromachining procedure. Optical, mechanical, and electrical simulations, together with the practical measurements, verify the application of our developed solar cells to be mounted on a limited-footprint and flexible SCL. The 15 μm-thick silicon solar cells conformally fit on a dome-shaped contact lens (ROC = 8 mm) without any mechanical and electrical degradation. This homojunction photovoltaic device containing an array of micro-holes exhibits a V oc, J sc, and maximum power density of 504 mV, 6.48 mA cm-2, and 1.67 mW cm-2, respectively, at 25% visible light transparency under an AM1.5 one sun condition. Furthermore, the measurements were conducted under low-intensity indoor light conditions and resulted in a maximum power output of 25 and 42 μW cm-2 for the 50 and 25% transparent solar cells, respectively.

Improvement in the light conversion efficiency of silicon solar cell by spin coating of CuO, ZnO nanoparticles and CuO/ZnO mixed metal nanocomposite material

Synthesis of pure Zinc oxide (ZnO), Copper oxide (CuO) nanoparticles (NPs) and their (ZnO/CuO) nanocomposites (NCs) in 1:1 M ratio were successfully prepared by co-precipitation method. The structural properties of the as synthesized nanoparticles and nanocomposite materials were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques. Optical band-gap studies were done using UV–Visible absorption spectroscopy. Photovoltaic properties of pure ZnO NPs, CuO NPs and ZnO/CuO NCs coated over a single-crystalline silicon solar cell were carried out to compare improvement of light-conversion efficiency in coated solar cell. The maximum light conversion efficiencies were found to be of 8.02% for CuO (3 mg/ml concentration) and 7.28% for ZnO NPs (3 mg/ml concentration), whereas that of mixed metal nanocomposite CuO/ZnO NCs was found to be 7.62%. at very low concentration of 1 mg/ml. This indicates with low concentration of mixed metal NCs an improvement in light efficiency can be obtained. The enhancement in efficiency could be due to formation of p - n heterojunction by CuO/ZnO NCs composites which enhances the number of electrons and holes participating in conduction on the surface.

Formation of inverted pyramid-like structures on surfaces of single crystalline silicon solar cells by chemical wet etching

We present a new, simple, and cost-effective etching method for forming inverted pyramid-like structures on the surfaces of single-crystalline diamond-wire sawn silicon wafers. The method follows a three-step process for etching silicon wafers without metal-assisted chemical etching involved. We used acidic etching to produce nano-to-micro-structured caves in the first two steps followed by anisotropic etching with an alkaline solution. This paper shows that the size of the opening of the inverted pyramid could vary from several hundred nanometers to about 4 μm, depending on the etch time periods in the second and the third steps. The cell performance was, however, only evaluated here for cases of smaller sizes of inverted pyramids. That is, solar cells were manufactured following an almost commercially standard procedure by using wafers with inverted pyramids of ∼900 nm in size. The best cell with this type of structure has a conversion efficiency of 19.22%, which is higher relative to the cells with smaller inward recessed caves or upright pyramids on the surfaces.

Ag and Cu metal-assisted chemical etching for diamond-wire-sawn single-crystalline silicon solar cell

In the present study, Ag and Cu metal-assisted chemical etching (MACE) technique was used for etching single-crystalline silicon at 15–25 °C, followed by post-processing with the HF/HNO3/H2O solution. Further, the relationship between the shape of the cross-section of the pore and the quality of passivation was deciphered. The parameters Jo1, minority carrier lifetime, and surface recombination velocity were measured, and the correlation between these three parameters and the open-circuit voltage (Voc) value was determined for all solar cells. The changes in the reflectance, solar flux density, and external quantum efficiency with changing wavelength were analyzed, and the relationship of these changes with short-circuit current density was determined. The Voc of all Ag-MACE solar cells is greater than that of all Cu-MACE solar cells, although the efficiency of almost all Cu-MACE solar cells is higher than that of the Ag-MACE solar cells. Furthermore, the electroluminescence image, the adhesion between the silver electrode and the pore, the quality of the aluminum back surface field, the metal residues on the surface, and the bulk of the wafer were systematically investigated. The best solar cell efficiency obtained for Ag-MACE and Cu-MACE PERC structures was 18.68% and 19.32%, respectively.

Fabrication of inverted pyramid structure for high-efficiency silicon solar cells using metal assisted chemical etching method with CuSO4 etchant

Inverted pyramid texture is used to improve the performance of single crystalline silicon (sc-Si) solar cell due to its excellent light-trapping properties. In this paper, inverted pyramid structures are fabricated on large area sc-Si wafers by metal assisted chemical etching method using CuSO 4 instead of Cu(NO 3 ) 2 . Three groups of solar cells were fabricated with textured structures prepared by CuSO 4, Cu(NO 3 ) 2 and NaOH respectively. The surface microstructure, average reflectivity, surface recombination and auger recombination, internal quantum efficiency and external quantum efficiency of the sc-Si solar cells were studied in detail. The results show that CuSO 4 can prepare uniform inverted pyramid structures on silicon substrate by reducing the generation of bubbles and promoting the deposition copper nano-particles on the surface of sc-Si wafer, and thus improve the properties of solar cells. More importantly, the chemical reaction mechanism for etching silicon wafer with CuSO 4 and Cu(NO 3 ) 2 during the texturing process was compared and analyzed. Finally, the average efficiency of large-area sc-Si PERC solar cells fabricated by CuSO 4 was 22.63%, which was 0.60% absolutely higher than that of Cu(NO 3 ) 2 , and 1.56% higher than normal pyramid group.

Enhancement of the Silicon Solar Cell Efficiency by Spin-Coated Polythiophene Films Embedded with Gold or Palladium Nanoparticles on the Rear Contact.

In this article, we investigate the application of polythiophene (PT), polythiophene with embedded gold nanoparticles (PT-Au), and polythiophene with embedded palladium nanoparticles (PT-Pd) via the spin coating technique on the rear contact of single-crystalline silicon solar cells. Several layers of coating (up to four layers) were applied, followed by a simple heat treatment at 70 °C for 30 min. The morphology, particles distribution in the polymer, and crystal structure of the colloid PT, PT-Au, and PT-Pd were characterized by transmission electron microscopy (TEM). Optical characteristics of the polymer and nanoparticles embedded in the polymers exhibited high absorption in the near-UV region, and a plasmonic peak at around 580 nm is observed. The calculated energy gap ranged from 2.65 eV (PT-Pd 5%) to 2.9 eV (PT) and 3.05 eV (PT-Au 5%). Scanning electron microscopy (SEM) images of the successive layers show an increase in the density and thickness of the PT particles with increasing number of coating layers, up to 12 μm for four layers of PT. Devices were characterized under dark conditions exhibiting variations in the ideality factor and series and shunt resistances with different coating layers. The silicon solar cells were characterized by measuring quantum efficiency, photoconversion efficiency (PCE), fill factor, and series and shunt resistances before and after coating. The coating was found to reduce the series resistance and to increase the efficiency of the cell by up to 7.25% for the PT-Au5% layers.

Large-scale preparation of 22.06% efficiency single-crystalline silicon solar cells with inverted pyramid microstructure through nanostructure rebuilding treatment

The inverted pyramid microstructures (IPMS) were fabricated jointly by metal-assisted chemical etching (MACE) technology with extremely low concentration of silver ions to formed nanopores and nanostructure rebuilding (NSR) treatment of NH4HF2 solution. The results show nanopores were achieved with the aid of Ag-MACE technology, which diameter was mainly affected by the action of Ag ions, and depth was yet mainly influenced by HF concentration. Textured IPMS single-crystalline silicon (sc-Si) solar cells with the diameter of 1 μm and reflectivity of 8.62% were large-scale prepared. Benefiting from better light-trapping ability, the photoelectric conversion efficiency of IPMS sc-Si solar cells in standard size of 156.75 × 156.75 mm2 achieved 22.06%. Simultaneously, the short-circuit current was increased by 71 mA. This promising technology could become a viable solution for industrial production of highly efficient sc-Si solar cells in the foreseeable future.

Effect of Plasmonic Nanoparticles on the Electric Field Strength to Improve Performance of Single Crystalline Solar Cell

The effect of metal nanoparticles (MNPs) on the electric field strength and distribution for improvement solar cell performance is investigated and simulated. By manipulating the properties of nanoparticles, distribution of the electric field was altered. In this paper, classical solar cell (p-n junction) and improved structure (add an extra layer of SiO2 and gold nanoparticles on the top of p-n junction) is simulated. Different sizes of NPs, thickness of SiO2 sublayer, and spacing distance between NPs is done to improving the electric field and showing plamonic effect. Gold NPs deposition on single crystalline silicon solar cell is modelled by COMSOL 5.2 2D, Electromagnetic wave propagation in the frequency domain with periodic boundary conditions. The best wavelength found in our work is 550 nm. The electric field enhances when the size of NPs increases but it must be limited. When gold NPs are deposited on the SiO2 sublayer, the plasmonic effect appears due to decreasing the refractive index. Moreover, separation distance between NPs affect the electric field enhancement by manipulating the number of NPs, the distance decreases and the plasmonic interaction appears.

Thermal and angular dependence of next‐generation photovoltaics under indoor lighting

AbstractNext‐generation photovoltaic technologies such as dye‐sensitized solar cells, organic thin‐film photovoltaics and perovskite solar cells are promising to efficiently harvest ambient light energy. However, more and deeper understanding of their photovoltaic characteristics is essential to create new applications under room light illumination. In this study, for the first time, the difference in temperature coefficients and angular dependence of photovoltaic parameters for the large‐area devices are investigated systematically under the compact fluorescent lamp and light‐emitting diode light. These emerging photovoltaic devices, compared with the single crystalline silicon solar cells, not only have higher open‐circuit voltage (up to approximate 1 V) and better power conversion efficiency (in the range of 9.2% ~ 22.6%) but also exhibit less temperature dependent voltage and output power (< −0.6% °C−1), as well as broader angular response (over 75 degrees). The state‐of‐the‐art dye‐sensitized and organic thin‐film devices also show advantageously positive temperature coefficients of current, and the latter even has positive thermal dependence of fill factor. These features suggest the next‐generation photovoltaic devices are more favorable than the conventional crystalline silicon solar cells for real‐life indoor applications.

Insight into Al–Si interface of PERC by Kelvin probe force microscopy

Passivated emitter and rear cell (PERC) has the advantage of higher short circuit current and open circuit voltage, which are generally claimed to be related to the reduction of rear side recombination and the increase of rear surface reflection. However, few works have focused on exploring the internal conducting mechanism about it. Herein, the influence of PERC technique on improving the short circuit current is investigated by comparing a PERC with a single crystalline silicon (sc-Si) solar cell. The surface potential results measured by Kelvin probe force microscopy show a higher surface potential step at the Al–Si interface of PERC than that of sc-Si cell, indicating a severe energy band variation and a better carrier collecting ability of PERC. Moreover, by using advanced microstructure characterization techniques, the relationship among the surface potential step, morphology and element distribution is fully studied, which proposes a new viewpoint to explain the enhanced performance of PERC.

Hard mask processing of 20% efficiency back-contacted silicon solar cells with dopant-free heterojunctions

Single junction crystalline silicon (c-Si) solar cells featuring a conventionally doped interdigitated back contact heterojunction (IBC-SHJ) structure has approached a record efficiency of 26.6%, which is very close to the practical limit. However, integrating the interdigital p- and n-type amorphous silicon (a-Si:H) layers on the rear surface of Si substrate is of such complexity, posing problem of heavy dependences on expensive manufacturing techniques including plasma-enhanced chemical vapor deposition and photolithography. Its commercial potential is thus always being questioned, and to seek an alternative fabrication procedure, which adapts to cost-effective deposition parallel with simple patterning characteristics, has been a primary research target of related subjects. Here, we demonstrated 20.1% efficiency dopant-free IBC-SHJ solar cells by combining evaporated carrier-selective materials (MoOx and LiFx) and two-steps hard masks alignments, delivering substantial simplifications in the architecture and fabrication procedures. We investigated the effect of intrinsic a-Si:H films with different thicknesses on the passivation and contact resistance for both a-Si:H/MoOx and a-Si:H/LiFx contacts, showing 4 nm a-Si:H is better for high efficiency IBC-SHJ solar cells. We also found that the position of the metal target (electrode definition step) and isolation in between the busbar and the Si substrate are highly relevant to leakage and recombination and have great impact on the device performance. The dopant-free IBC-SHJ solar cells demonstrated here manifest enough confidence in our hard mask based fabrication procedure, with great potential for high performance-to-cost ratio in future.

Efficiency improvement of Si solar cells by down-shifting Ce3+-doped and down-conversion Ce3+-Yb3+ co-doped YAG phosphors

Down-shifting and down-conversion processes are an effective way to improve the poor response of single crystalline silicon (c-Si) solar cells at shorter wavelength region. The Ce3+-doped YAG possesses a down-shifting (DS) process which converts ultra-violet (UV) and blue light into yellow light whereas Ce3+-Yb3+ co-doped YAG exhibits a down-conversion (DC) process which converts UV and blue light into both yellow as well as near-infrared (NIR) light. In this paper, Ce3+-doped YAG and Ce3+-Yb3+ co-doped YAG phosphors are mixed with ethyl vinyl-acetate and then coated on the top surface of c-Si solar cells by using spin-coating method. The solar cells enhance the energy conversion efficiency from 15.71% to 16.06% (Δη = 2.23%) and 15.96% to 16.63% (Δη = 4.19%) for DS and DC process, respectively. The experimental results demonstrated that these types of phosphors are promising candidates for enhancing the performances of c-Si solar cells in practical application.

Low-cost and low-temperature chemical oxide passivation process for large area single crystalline silicon solar cells

Although thermally grown silicon dioxide is an excellent surface passivation layer for Si wafers, its industrial applicability for solar cell surface passivation is limited due to low throughput and high cost. This has prompted the exploration of low temperature and chemical silicon dioxide processes for silicon solar cells. In this work, a low-cost, low-temperature (40 °C), non-acidic and safe chemical oxide passivation process (named as NCPRE-oxide) with only sodium hypochlorite (NaOCl) solution is proposed and investigated on large area wafers (125 mm × 125 mm). This process uses a single-component chemical solution to grow ultra-thin silicon oxide (SiOx) layer of thickness of about 1.5 nm. The chemical SiOx layer capped with hydrogenated amorphous silicon nitride (SiNx:H) improves passivation on the n-type silicon surface. A considerable enhancement in the effective minority carrier lifetime (τeff) is observed for SiNx:H/SiOx stack on the phosphorous diffused pyramidal textured silicon surface. The versatility of the NCPRE-oxide is verified by transmission electron microscopy, ellipsometry, X-ray photoelectron spectroscopy, effective minority carrier lifetime and photoluminescence imaging measurements. The introduction of present SiNx:H/SiOx stack in our baseline cell fabrication process resulted in the improvement in cell efficiency by 0.3% (absolute) for screen-printed full area aluminum back surface field cells.

Rear-surface line-contact optimization using screen-print techniques on crystalline solar cells for industrial applications

This paper explores the utility of single-crystalline silicon solar cells that are treated with the screen-print technique to implement line contacts at the cells’ rear surfaces. We designed rear-surface line-contact (RSLC) solar cells using screen-print methods on n-type wafers (125 ×125 mm2) in order to produce rear surface passivation layers. The performances of these cells were then evaluated and compared to laser fired contact solar cells. We examined the rear surface passivation quality of a stack consisting of an aluminum oxide (Al2O3) passivation layer deposited by atomic layer deposition, overlaid with a silicon nitride (Si3N4) layer deposited by plasma-enhanced chemical vapor deposition. The initial outstanding surface passivation quality provided by the Al2O3/Si3N4 stacks remained high after annealing, as indicated by the average light-beam-induced-current value (85.1 mA/cm2) for the developed RSLC cells. RSLC cells exhibited conversion efficiencies of up to the optimal 18.48%, demonstrating that line-contacting processes were consistent with print screen and that the simplification of electrode process may be realized for industrial applications.

Acoustically driven degradation in single crystalline silicon solar cell

The influence of ultrasound on current–voltage characteristics of crystalline silicon solar sell was investigated experimentally. The transverse and longitudinal acoustic waves were used over a temperature range of 290–340 K. It was found that the ultrasound loading leads to the reversible decrease in the photogenerated current, open–circuit voltage, fill factor, carrier lifetime, and shunt resistance as well as the increase in the ideality factor. The experimental results were described by using the models of coupled defect level recombination, Shockley–Read–Hall recombination, and dislocation–induced impedance. The contribution of the boron-oxygen related defects, iron-–boron pairs, and oxide precipitates to both the carrier recombination and acousto–defect interaction was discussed. The experimentally observed phenomena are associated with the increase in the distance between coupled defects as well as the extension of the carrier capture coefficient of complex point defects and dislocations.

Facile fabrication method of small-sized crystal silicon solar cells for ubiquitous applications and tandem device with perovskite solar cells

Small-sized single crystalline silicon solar cells (ca. 25 mm2) were fabricated by a non-vacuum process as an energy supply for small devices (ubiquitous devices: a wristwatch, desktop calculator etc.) and processed for a tandem solar-cell research. A side-edge etching procedure was performed in order to eliminate detrimental cracks to improve photovoltaic properties. Moreover, the new structure of the small-sized solar cell with side contact provides reduced shadow loss of contacts. After the structural and procedural optimization, a conversion efficiency of 16.4% was achieved by a non-vacuum process with 3 mm × 8 mm surface dimension solar cell. Finally, the photovoltaic characteristics of small silicon cells, as a function of light intensity for the ubiquitous purposes were compared with amorphous silicon solar cells. In addition, the facile processed silicon solar cell was integrated into mechanically-stacked tandem solar cells with perovskite solar cells by direct contact of TCO layers of each sub-cell. The counter electrode MoOX/IZO over HTM (spiro-OMeTAD) in top perovskite cells is physically placed on top of the bottom Si solar cell to form a series tandem configuration.

Perovskite Nanopillar Array Based Tandem Solar Cell

One of the promising approaches to improve the efficiency of conventional single-crystalline silicon (c-Si) solar cells is their integration in a tandem arrangement. In this perspective, inorganic–organic perovskites are an ideal blend of materials to combine with c-Si owing to their complementary light absorption characteristics. Even though interesting and promising combinations of perovskite/c-Si-based solar cells have been presented, their overall efficiency has been limited by the photocurrent reduction occurring in both perovskite and silicon due mostly to reflection and parasitic losses. Here, we envision and model a new design strategy for an efficient light-to-current conversion through the use of a nanopillar array based perovskite/c-Si tandem solar cell. The optical–electrical performance of the proposed architecture is analyzed by a 3D finite-element numerical model. In particular, we have searched for the best optical enhancement conditions through the tuning of the cell geometrical parameter...

Investigation of shunt solar cells’ currents based on equivalent circuit model

In view of the universality of the parallel connection of solar cells and their mismatch problem, in the present paper, we select two shunt solar cells (connected in parallel) as our research object, and use the equivalent one-diode circuit of the solar cell and the analysis of the two-body model. At first, the equations of current and voltage are deduced from the related electrical laws and the circuit diagram of the two solar cells connected in parallel. Then, according to the experimentally measured data of typical single-crystalline silicon solar cells (125 mm×125 mm), we select the appropriate simulation parameters. Following this, by using the photo-generated current, the shunt resistance, and the serial resistance of one of the shunt solar cells and the load resistance as independent variables, in turn, the changing characteristics of each branch current in the two shunt solar cells are numerically discussed and analyzed for these four cases for the first time. At the same time, we provide a simple physical explanation for the modeling results. Our analyses show that these parameters have different impacts on the internal currents of solar cells connected in parallel. These results provide a reference to solve the problem of connecting solar cells and to develop higher efficiency solar cells and systems. Meanwhile, the results will contribute to a better comprehension of the reasons for efficiency loss of solar cells and systems, and deepen the understanding of the electrical of solar cells behavior for high performance photovoltaic applications.