Junction Solar Cells Research Articles

High efficiency perovskite/heterojunction crystalline silicon tandem solar cells: towards industrial-sized cell and module

29.2%-conversion efficiency of a two-terminal (2T) perovskite/crystalline Si heterojunction tandem solar cell using 145 μm thick industrial Czochralski (CZ) Si wafer is obtained. The structural optimization, such as surface passivation of the perovskite layer and better light management techniques, improved power conversion efficiency (PCE). To our knowledge, this PCE is the best in 2T-tandem solar cells using CZ wafers. Towards industrialization, crucial issues with the 2T tandem solar cells with crystalline Si bottom cell are discussed. Four-terminal (4T) tandem solar cells are evaluated as an approach to avoid the crucial issues. Examining our base technologies which realize 22.2%-conversion efficiency perovskite single junction solar cell module and 26%-heterojunction back-contact solar cells, we clarified that the based technologies were ready to realize 30%-conversion efficiency 4T perovskite/heterojunction crystalline Si tandem solar cells with approximately quarter size of an industrial crystalline Si solar cell (∼64 cm2).

All-Perovskite Tandem Solar Cells: From Certified 25% and Beyond

Perovskite-based solar cells are a promising photovoltaic technology capable of offering higher conversion efficiency at low costs compared with the standard of the market. They can be produced via a thin film technology that allows for considerable environmental sustainability, thus representing an efficient, sustainable, flexible, and light solution. Tandem solar cells represent the next step in the evolution of photovoltaics (PV). They promise higher power conversion efficiency (PCE) than those currently dominating the market. The tandem solar cell design overcomes the limitations of single junction solar cells by reducing the thermal losses as well as the manufacturing costs. Perovskite has been employed as a partner in different kinds of tandem solar cells, such as the Si and CIGS (copper indium gallium selenide) based cells that, in their tandem configuration with perovskite, can convert light more efficiently than standalone sub-cells. This brief review presents the main engineering and scientific challenges in the field. The state-of-the-art three main perovskite tandem technologies, namely perovskite/silicon, perovskite/CIGS, and perovskite/perovskite tandem solar cells, will be discussed, providing a side-by-side comparison of theoretical and experimental efficiencies of multijunction solar cells.

Fill Factor Loss in a Recombination Junction for Monolithic Tandem Solar Cells

Fill Factor Loss in a Recombination Junction for Monolithic Tandem Solar Cells

Bis(stearoyl) Sulfide: A Stable, Odor‐Free Sulfur Precursor for High‐Efficiency Metal Sulfide Quantum Dot Photovoltaics

AbstractThe synthesis of metal sulfide nanocrystals is a crucial step in the fabrication of quantum dot (QD) photovoltaics. Control over the QD size during synthesis allows for precise tuning of their optical and electronic properties, making them an appealing choice for electronic applications. This flexibility has led to the implementation of QDs in both highly‐efficient single junction solar cells and other optoelectronic devices including photodetectors and transistors. Most commonly, metal sulfide QDs are synthesized using the hot‐injection method utilizing a toxic, and air‐ and moisture‐sensitive sulfur source: bis(trimethylsilyl) sulfide ((TMS)2S). Here, bis(stearoyl) sulfide (St2S) is presented as a new type of air‐stable sulfur precursor for the synthesis of sulfide‐based QDs, which yields uniform, pure, and stable nanocrystals. Photovoltaic devices based on these QDs are equally efficient as those fabricated by (TMS)2S but exhibit enhanced operational stability. These results highlight that St2S can be widely adopted for the synthesis of metal sulfide QDs for a range of optoelectronic applications.

Characterization of various tandem solar cells: Protocols, issues, and precautions.

In the search for a more efficient solar cell, various types of tandem solar cells (TSCs) have been actively developed worldwide as the performances of the single junction solar cells approach their theoretical limits. Meanwhile, various materials and structures are adopted in TSCs, which makes their characterizations and comparison difficult. Along with the classical monolithic TSC, which exhibits two electrical contacts, devices with three or four electrical contacts have been widely studied as a more performing alternative of commercialized solar cells. For a fair and accurate evaluation of the device performance of TSCs, understanding the effectiveness and limitations of the characterization of the different types of TSCs is crucial. In this paper, we summarize various types of TSCs and discuss their characterization methods.

Thermal annealing effects on graphene/n-Si Schottky junction solar cell: removal of PMMA residues

Thermal annealing is one of the most effective ways to improve the efficiency of a graphene/n-Si Schottky junction solar cell. Here, its underlying mechanism has been investigated by comparative studies in terms of the removal of polymethyl methacrylate (PMMA) residues, using the J–V characteristics and transient photocurrent and photovoltage measurements. The obtained results have revealed that there are trap states that originate from the PMMA residues and cause the large photocurrent leakage as the intensity of the incident light increases. It is also found that the PMMA residues accelerate deterioration and rapidly invalidate hole doping effects. Such undesirable PMMA residues were effectively removed by the thermal annealing treatments, serving to reduce the photocurrent leakage and increase the stability.

Performance evaluation of lead free CH3NH3SnI3/GeTe Tandem solar cell with HTL layer by SCAPS 1D

In this article, with the help of a one dimensional solar cell simulator, we have assessed different performance parameters of a lead free CH3NH3SnI3/GeTe Tandem solar cell. The performance parameters in terms of open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and photo conversion efficiency (PCE) have been investigated for different thickness of absorber layer, acceptor concentration, defect density and series/shunt resistance and compared with a single junction solar cell. Incorporation of GeTe as a secondary absorber layer improves the performance of the solar cell by increasing photon absorption rate. Using Cu2O as a hole transport layer, formation of a quantum well takes place which further enhances the photon absorption rate and hence solar cell performance. The optimized tandem cell with hole transport layer shows 28 %, 9 %, 19 % and 12 % improvement in Voc, Jsc, FF and PCE compared to the single junction solar cell without hole transport layer.

Boosting efficiency and stability with KBr interface modification for NiOx-based inverted perovskite solar cells

NiOx-based inverted structure perovskite devices possess advantages in the application of single junction and tandem solar cells. However, energy loss and instability originating from interface defects commonly result in inferior device performance. Herein, Potassium Bromide (KBr), as a buffer layer, was inserted between the perovskite and NiOx hole transport layer to modify the interface. The valence band maximum of NiOx improved to −5.37 eV which matches better with perovskite. The lifetime of hot carriers and intrinsic charge recombination revealed by Femtosecond transient absorption spectroscopy (fs-TAS) confirm that KBr modification can facilitate charge separation. Benefiting from the improvement of perovskite quality which results from K+ diffusion and enhanced charge transport, the power conversion efficiency (PCE) of the modified device reaches up to 19.21%, whereas the pristine is 17.56%. Meanwhile, the air stability of the unencapsulated device also improved dramatically, which maintains 80% of its initial PCE after 1100 h high humidity storage. This work unambiguous reveals the mechanism of perovskite/NiOx interface modification and provides a facile and effective strategy for interface optimization.

Bandgap engineered 1.48 eV GaAs0.95P0.05 solar cell with enhanced efficiency using double BSF layer

One of the most important criteria to design more than 30% efficient III–V compound/Si based dual junction solar cell is that we must design atleast 20% efficient III–V compound material top cell. In this regard, we designed a bandgap engineered GaAs0.95P0.05 single junction solar cell with reduced bandgap of (E g ) = 1.48 eV. Reducing the bandgap from 1.72 eV to 1.48 eV for GaAs0.95P0.05 cell leads to generate higher short circuit current, while having the tradeoff with the open circuit voltage. Due to small change in lattice constant of GaAs0.95P0.05 cell, some recombination is observed near the junction area. Although the minimal degradation is observed in open circuit voltage, the higher short circuit current drives the overall efficiency of the GaAs0.95P0.05 single junction solar cell. The designed solar cell provides an extended internal absorption for longer wavelength of spectrum. The high electron mobility of 8500 cm2 V–S−1 was observed with very high electron to hole mobility ratio of 21.25. The optimization of the cell is done using two back surface field layers (AlInP and AlGaInP) of higher bandgap material. The high short circuit current density of J SC = 25.93 mA cm−2 with V OC = 1.1635 V achieved by the designed cell with the highest efficiency of η = 25%. The solar cell is irradiated under 1-Sun solar irradiation in the AM1.5 G environment providing 1000 W m−2 of power spectral density. The External and Internal Quantum efficiency of more than 95% is achieved by the designed solar cell.

Low energy muon study of the p-n interface in chalcopyrite solar cells

The slow muon technique was used to study the p-n junction of chalcopyrite solar cells. A defect layer near the interface was identified and the passivation of the defects by buffer layers was studied. Several cover layers on top of the chalcopyrite Cu(In,Ga)Se2 (CIGS) semiconductor absorber were investigated in this work, namely CdS, ZnSnO, Al2O3 and SiO2. Quantitative results were obtained: The defect layer extends about 50 nm into the CIGS absorber, the relevant disturbance is strain in the lattice, and CdS provides the best passivation, oxides have a minor effect. In the present contribution, specific aspects of the low-energy muon technique in connection with this research are discussed.

Developed graphene/Si Schottky junction solar cells based on the top-window structure

Developed graphene/Si Schottky junction solar cells based on the top-window structure

Large-area 11.75% efficient vertical graphene nanowalls/textured silicon Schottky junction solar cell based on PEDOT:Nafion doping scheme

Preparing large areas of graphene on textured silicon is necessary for the industrialization of graphene/silicon solar cells. However, many passivation films with insulating properties prepared by the solution method are not applicable for the textured structures as the insulation areas are easily formed at the bottom of the pyramid. In this paper, we prepare large-area vertical graphene nanowalls (VGNWs) on textured c-Si by plasma-enhanced chemical vapor deposition (PECVD) and introduce conductive-passivating poly(3,4-ethylenedioxythiophene) (PEDOT):Nafion composite thin films to modify the textured VGNWs/Si Schottky junction. The formation of insulation areas was avoided. Moreover, the reflectivity was reduced to less than 7% as the superposition of textured structures and PEDOT:Nafion film. After applying an interfacial layer of Al2O3, the cell efficiency was increased to 11.75%, with a large active area of 0.64 cm2. This work will promote the industrialization of VGNWs/Si solar cells.

Current transport characterization and photovoltaic performance of Si nanopencil-based Schottky junction assisted with VOx as a hole-injection layer

Pencil-shaped silicon nanowires (SiNPs) were utilized in Schottky junction solar cells covered by sub-stoichiometric vanadium dioxide (VO2-x) to work as a hole injection layer. The asymmetry of nanopencils is responsible for their many useful properties, such as their ability to absorb and trap light over a wide spectrum. Dark current-voltage (I–V) curves for an Ag/VO2-x/SiNPs/Ti/Ag Schottky junction device were measured and analyzed across a temperature range of 298–358 K. The junction parameters were calculated in terms of thermionic emission theory at different temperatures from the (I–V) curves, including the ideality factor (n) and the barrier height (φb), and were found to be 1.73 and 0.78 eV, respectively, at room temperature. In the forward bias regime, we found that thermionic emissions dominate at low voltages (V ≤ 0.12 V), space-charge-limited current controlled by a single trap state dominates at middle voltages (0.12 < V < 0.3 V), and space-charge-limited current regulated by a distribution of trap levels dominates at high voltages (V ≥ 0.3 V). The (C–V) measurements were used to calculate the built-in potential, which was discovered to be 0.62 eV. Unless encapsulation is provided, PEDOT:PSS/SiNPs hybrid solar cells rapidly degrade under ambient conditions, whereas VO2-x/SiNPs solar cells are far more stable.

Fabrication and Characterization of p-SnS/n-Si Solar Cell by Thermal Evaporation Technique and the Effect of Ag-doped on Its Efficiency

Tin sulfide (SnS) is a promising material for solar cell absorber layer applications due to its low cost, ease of availability and lower toxicity than other semiconductor materials, used for the same purpose. Thermal evaporation was used to deposit thin-film solar cells with SnS on glass and silicon substrates, with minimal silver doping ratios (0.02, 0.04 and 0.06) wt.% and thickness in the 125-nm range. Surface morphology, crystallite size and optical and electrical characteristics have all been thoroughly investigated. XRD analysis revealed that /both the undoped and Ag-doped SnS films were well crystallized, with an orthorhombic structure and polycrystalline nature. The (111) plane was the preferred orientation. Due to the low doping ratios, there are no silver-specific peaks. Additionally, the Scherer formula was used to calculate the crystallite size, which showed an increase from 3.7096 to 10.4716[Formula: see text]nm. AFM images showed that SnS: Ag (6[Formula: see text]wt.%) film has bigger grains than other samples. The Hall Effect test revealed that the film is p-type conductivity. The optical bandgap values were found to be in the (2.6–1.7[Formula: see text]eV) range. All of the SnS films had an absorption coefficient of more than [Formula: see text] above the fundamental absorption edge. These polycrystalline and highly absorbing SnS thin films can be used to make heterojunction solar cells. The wider energy gap of the produced films, which allows more light to reach the solar cell junction, was found to be connected to changes in thin film microstructure characteristics. The efficiency of the prepared solar cells reached 5.4% for the 6[Formula: see text]wt.%Ag-doped SnS/Si solar cell, with a fill factor of 0.46.

Cs2XI2Cl2 (X = Pb, Sn) All‐Inorganic Layered Ruddlesden–Popper Mixed Halide Perovskite Single Junction and Tandem Solar Cells: Ultra‐High Carrier Mobility and Excellent Power Conversion Efficiency

Layered pseudo‐2D perovskites are new and emerging candidates for optoelectronic applications, exhibiting excellent physical properties and very high stability compared to bulk perovskite structures. Herein, two synthesized inorganic layered perovskites with Ruddlesden–Popper phase Cs2XI2Cl2 (X = Pb, Sn) are investigated. The optoelectronic properties of these structures are calculated using density‐functional theory (DFT). In addition, single junction solar cells and a Cs2PbI2Cl2/Cs2SnI2Cl2 tandem cell, are investigated using the finite‐difference time‐domain method and drift‐diffusion model. The optimal absorption coefficient and suitable bandgap for solar cells are indicated by the results obtained from DFT. Based on the deformation potential theory, the ultrahigh charge‐carrier mobility of 104 order are predicted for these structures, which is much higher than the mobility of 3D known organic perovskites. Remarkable power conversion efficiencies of 24.09% and 21.94% for Cs2SnI2Cl2 and Cs2PbI2Cl2 solar cells, respectively, are shown in the calculated results, which are among highest reported efficiencies for layered perovskite solar cells. Also, the simulated tandem cell achieves a high open‐circuit voltage (Voc) of 1.68 V, which is higher than the Voc of single‐junction cells. The high potential of inorganic layered perovskites in optoelectronic devices with excellent efficiency and long‐term stability is implied by the obtained results.

High-performance vertical graphene nanowall/silicon Schottky junction solar cells with Nafion doping and plasma etching

In this paper, a solar cell based on the vertical graphene nanowall (VGNW)/silicon Schottky junction is doped by polymeric acid (Nafion) and exhibits a high power-conversion efficiency after Ar plasma etching. It is found that, the Nafion doping scheme effectively increases the WF of VGNW films by ∼0.5 eV, and simultaneously reduces its average reflectance to ∼28%. However, there appears to be a poor-conductive Nafion capping layer on the VGNWs after doping, which severely influences the carriers electrical transportation. When a plasma etching process is introduced, the VGNWs buried in the Nafion polymers are exposed, thus reducing its sheet resistance by ∼20%. The combination of Nafion doping and plasma etching makes the Vbi of the VGNW/n-Si heterojunction greatly improve and exceed 0.6 V, and the FF factor of the VGNW/n-Si solar cells increases from 55.8% to 62.9%. Applying interface passivation and light management, we achieve a significant gain of Jsc and a well-performance VGNW/n-Si Schottky junction solar cell (Voc of 523 mV, FF of 57.1% and Jsc of 30.8 mA/cm2), whose PCEs up to 9.2% (AM 1.5 G). The present device architecture design and optimisation scheme here are envisaged to be potentially valuable for the doping modification of other 3D materials with similar structures.

Advances in solar energy harvesting integrated by van der Waals graphene heterojunctions.

Graphene has garnered increasing attention for solar energy harvesting owing to its unique features. However, limitations hinder its widespread adoption in solar energy harvesting, comprising the band gapless in the molecular orbital of graphene lattice, its vulnerability to oxidation in oxidative environments, and specific toxic properties that require careful consideration during development. Beyond current challenges, researchers have explored doping graphene with ionic liquids to raise the lifespan of solar cells (SCs). Additionally, they have paid attention to optimizing graphene/Si Schottky junction or Schottky barrier SCs by enhancing the conductivity and work function of graphene, improving silicon's reflectivity, and addressing passivation issues at the surface/interface of graphene/Si, resulting in significant advancements in their power conversion efficiency. Increasing the functional area of graphene-based SCs and designing efficient grid electrodes are also crucial for enhancing carrier collection efficiency. Flaws and contaminants present at the interface between graphene and silicon pose significant challenges. Despite the progress of graphene/Si-based photovoltaic cells still needs to catch up to the efficiency achieved by commercially available Si p-n junction SCs. The low Schottky barrier height, design-related challenges associated with transfer techniques, and high lateral resistivity of graphene contribute to this performance gap. To maximize the effectiveness and robustness of graphene/Si-based photovoltaic cells, appropriate interlayers have been utilized to tune the interface and modulate graphene's functionality. This mini-review will address ongoing research and development endeavors using van der Waals graphene heterojunctions, aiming to overcome the existing limitations and unlock graphene's full potential in solar energy harvesting and smart storage systems.

Photoinduced interfacial electron transfer from perovskite quantum dots to molecular acceptors for solar cells.

Bandgap-engineered inorganic and hybrid halide perovskite (HP) films, nanocrystals, and quantum dots (PQDs) are promising for solar cells. Fluctuations of photoinduced electron transfer (PET) rates affect the interfacial charge separation efficiencies of such solar cells. Electron donor- or acceptor-doped perovskite samples help analyze PET and harvest photogenerated charge carriers efficiently. Therefore, PET in perovskite-based donor-acceptor (D-A) systems has received considerable attention. We analyzed the fluctuations of interfacial PET from MAPbBr3 or CsPbBr3 PQDs to classical electron acceptors such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 1,2,4,5-tetracyanobenzene (TCNB) at single-particle and ensemble levels. The significantly negative Gibbs free energy changes of PET estimated from the donor-acceptor redox potentials, the donor-acceptor sizes, and the solvent dielectric properties help us clarify the PET in the above D-A systems. The dynamic nature of PET is apparent from the decrease in photoluminescence (PL) lifetimes and PL photocounts of PQDs with an increase in the acceptor concentrations. Also, the acceptor radical anion spectrum helps us characterize the charge-separated states. Furthermore, the PL blinking time and PET rate fluctuations (108 to 107 s-1) provide us with single-molecule level information about interfacial PET in perovskites.

Research progress of perovskite/crystalline silicon tandem solar cells with efficiency of over 30%

Double junction tandem solar cells consisting of two absorbers with designed different band gaps show great advantage in breaking the Shockley-Queisser limit efficiency of single junction solar cell by differential absorption of sunlight in a wider range of wavelengths and reducing the thermal loss of photons. Owing to the advantages of adjustable band gap and low cost of perovskite cells, perovskite/crystalline silicon tandem solar cells have become a research hotspot in photovoltaics. We systematically review the latest research progress of perovskite/crystalline silicon tandem solar cells. Focusing on the structure of perovskite top cells, intermediate interconnection layers and crystalline silicon bottom cells, we summarize the design principles of high-efficiency tandem devices in optical and electrical aspects. We find that the optical and electrical engineering of each layer structure in perovskite/crystalline silicon tandem solar cells goes through the whole process of device preparation. We also summarize the challenges of limiting the further improvement of the efficiency of the perovskite/crystalline silicon tandem solar cells and the corresponding improvement measures, which covers the following respects: 1) Improving the balance between &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;oc&lt;/sub&gt; and &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;sc&lt;/sub&gt; of the broadband perovskite cell through additive engineering and interface engineering; 2) improving the bandgap matching between the electrical layers and reducing the carrier transport barrier through adjusting the work function or conductivity of layers; 3) improving the photocurrent coupling between sub-cells and the photocurrent of tandem solar cells by using light engineering and conformal deposition technology of perovskite cells. At present, there have been many technologies to improve the stability of perovskite solar cells, such as additive engineering and interface engineering, but the problem has hardly been solved. Therefore, improving the stability of broadband gap perovskite solar cells to the level of crystalline silicon solar cells will become an important challenge to limit its large-scale application. In terms of efficiency, the mass production efficiency of perovskite/crystalline silicon tandem solar cells is far lower than that of the laboratory level. One of the reasons is that it is difficult to achieve low-cost and deposition of uniform large area perovskite solar cells. Therefore improving the stability of broadband gap perovskite solar cells and developing low-cost large-area perovskite deposition technology will become extremely critical. Finally we look forward to the next generation of higher efficient low-cost tandem solar cells. We believe that with the increasing demand for higher efficiency photovoltaic devices, the triple junction solar cells based on the perovskite/crystalline silicon stack structure will become the future photovoltaics.

TOPcon route with quantum wells in GaInP/Si dual junction cell for efficiency enhancement

The GaInP/Si dual junction solar cell with Quantum Well and TOPCon technology has achieved 41.91 % efficiency in the simulation model. Quantum wells are proven to enhance the short circuit current without any significant degradation of open circuit voltage. The voltage preservation measure (for minimum reduction in open circuit voltage) is applied in design of Quantum well solar cell with the improvement in short circuit current, therefore the overall efficiency of dual junction cell is enhanced. In this work, the GaInP/Si dual junction solar cell is proposed by incorporating the InP quantum wells in the p-i-n region of GaInP top cell. Also, the TOPCon technology is applied at the rear side of the bottom c-Si solar cell. The quantum well increases the absorption of sub-bandgap photon energy. The buffer layer reduces the misfits between the lattice mismatched layers and tunnel oxide provides excellent passivation mechanism to increase the open circuit voltage. The ultrathin oxide layer provides extremely high electric field as described by the MIS tunneling theory. The electron and hole bound state energy and wavefunctions provides “miniband” formation and charge carrier trapping. The formation of type-A band structure in quantum well region and excellent electron mobility results in enhanced carrier transport. The GaInP/Si integrated model achieves efficiency of 33.30 % when the quantum wells are incorporated in the top cell. When the Combination of both QWs (in top cell) and TOPCon technology (in bottom cell) is applied, the model achieves 41.95 % efficiency. This model provides an excellent route toward achieving the 45 % efficiency limit of III-V/Si dual junction 2-terminal solar cell. The industry standard Silvaco TCAD platform is used for the calculation of the performance characteristics in AM1.5G environmental condition.