Double-junction Tandem Solar Cells Research Articles

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 <i>V</i><sub>oc</sub> and <i>J</i><sub>sc</sub> 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.

New numerical model for a 2T-tandem solar cell device with narrow band gap SWCNTs reaching efficiency around 35 %

With a large-band gap top cell and a low-band gap bottom cell, double-junction tandem solar cells have a huge potential to exceed existing single-junction photovoltaic technology. To fully benefit, serious attention must go into the choice and performance amelioration of both cells. Tandem solar cells with two terminals (2 T) are highly efficient in converting energy. As the 2 T tandem solar cell configuration is equivalent to an electric series connection between the sub-cells, one of its key constraints is the circulation of current density. The monolithic device's performance is constrained because the sub-cell with the lowest current (top cell) forces it to run at its value. Using a bottom sub-cell made of Single-Walled Carbon Nanotubes (SWCNTs), which has an interesting current density and matches the top cell, is a possible solution for such a challenge as presented in this simulation work. The 2 T monolithic solar cell resulting from this study offers interesting photovoltaic parameters with an excellent fill factor and power conversion efficiency of 34.8 %.

Design and optimization of highly efficient perovskite/homojunction SnS tandem solar cells using SCAPS-1D

Double-junction tandem solar cells containing a wide-bandgap top cell and a narrow-bandgap bottom cell have a great potential to outperform current single-junction photovoltaic technologies. However, careful consideration is required in the selection and optimization of both sub-cells to obtain full benefit. In this study, we present numerical simulations of tandem solar cells with tin sulfide (SnS) bottom sub-cells and organic–inorganic lead halide perovskite top sub-cells using SCAPS-1D. The performance of SnS homojunction solar cell optimized by investigation of the p-type and n-type layer thicknesses, doping concentrations, defect densities, and interface defects. Afterward, the perovskite solar cell is optimized in terms of variation in absorber bandgap (1.55–1.75 eV) and thickness (100–800 nm). To properly simulate tandem devices, bottom cells are optically filtered by calculated spectra of perovskite solar cells. Current matching has been done by varying thickness of the perovskite sub-cell with different bandgaps, and the optimized 28.92% efficiency has been revealed for the perovskite/SnS tandem device. This is the first numerical simulation using homojunction SnS as a bottom sub-cell in perovskite tandem solar cells to the best of our knowledge. Results suggest that tin sulfide homojunction solar cells could be a low-cost and environmentally friendly bottom sub-cell for efficient perovskite tandem solar cells.

The optimization of CsPbIBr2 top sub-cells for the application in monolithic all-perovskite tandem solar cells

More and more attention has been paid to CsPbIBr2 material for perovskite solar cells (PSCs), owing to the trade-off between bandgap and stability. However, the reported maximum power conversion efficiency (PCE) of CsPbIBr2 PSCs is lag behind that of the congeners due to the serious interface recombination of charge carriers. In this work, the effects of interface defect density and interface band offset on the properties of CsPbIBr2 PSCs are investigated. It is found that the characteristic of the front electron transfer layer (ETL)/perovskite interface has a significant influence on the performance of PSCs than that of the back perovskite/hole transfer layer (HTL) interface. Additionally, a PCE of 15.05% with a high open-circuit voltage (VOC) of 1.54 V is obtained for the PSCs with FTO/ZnOS/CsPbIBr2/CuAlO2/Au structure. Finally, two-terminal monolithic all-perovskite double-junction tandem solar cells (TSCs) with the architecture of FTO/ZnOS/CsPbIBr2/CuAlO2/ITO/TiO2/MAPbI3/Spiro-MeOTAD/Au are constructed, and a maximum PCE of 27.4% (VOC of 2.60 V, JSC of 12.21 mA/cm2, and FF of 86.42%) is obtained for the TSCs with top and bottom absorber thicknesses of 600 nm and 500 nm respectively. Furthermore, four-terminal triple-junction TSCs are designed with silicon solar cells as bottom sub-cell, and a maximum PCE of 35.35% is achieved. These results will provide theoretical guidance for the fabrication of high performance TSCs.

Highly efficient wide-band-gap perovskite solar cells fabricated by sequential deposition method

Perovskite-based double junction tandem solar cells, including perovskite/silicon, perovskite/perovskite, and perovskite/Cu(In, Ga)Se 2 , have received increasing attention in recent years. While most wide-band-gap perovskite solar cells so far were synthesized by the one-step deposition method which has a simple procedure but is hindered by its narrow antisolvent dripping time window, exploration of other method is in demand. In this study, a highly efficient wide-band-gap perovskite solar cell device with a bandgap of 1.63–1.65 eV has been successfully fabricated using the two-step sequential deposition method by optimizing the solution composition and the spinning speed of the second step. The best solar cell obtained has a power conversion efficiency of 20.35% and a fill factor (FF) of 81.53%, and is believed to be the first wide-band-gap solar cell device fabricated by the sequential deposition method with an efficiency over 20%. The obtained FF value is also pretty high among all reported perovskite solar cells fabricated by sequential deposition method. Our work indicates that sequential deposition method not only can be applied to the traditional narrow-band-gap perovskite solar cells but also has a potential for fabricating highly efficient wide-band-gap perovskite solar cells. A highly efficient wide-band-gap perovskite solar cell device with an energy conversion efficiency of 20.35% and a fill factor of 81.53% has been successfully fabricated using the two-step sequential deposition method by optimizing the solution composition and the spinning speed of the second step. • A highly efficient wide-band-gap perovskite solar cell device was fabricated using sequential deposition method. • The obtained FF value 81.53% is the maximum among all reported perovskite solar cells fabricated by sequential deposition method. • This work has shown the potential of sequential deposition method for fabricating highly efficient and reproducible wide-band-gap perovskite active layers.

Thermodynamic limit of tandem solar cells under different solar spectra and their perovskite top solar cell

Abstract Thermodynamic (detailed balance) limits of single-junction and tandem-type solar cells are calculated under different solar spectra, which are spectra of blackbody (6000 K), air mass 0, air mass 1.5 global (1.5G), and air mass 1.5 direct (1.5D). The solar cells are described by blackbody under room temperature of 298.15 K. It is disclosed that optimized bandgaps of single-junction solar cells with the highest conversion efficiencies of 31.6, 30.6, 33.7 and 33.1% are 1.29, 1.25, 1.34, and 1.34 eV under illuminations of blackbody (6000 K), air mass 0, air mass 1.5G, and air mass 1.5D, respectively. Conversion efficiencies of 43.2, 42.2, 45.5, and 45.1% are further increased for double-junction tandem solar cells with optimized bandgaps of bottom and top cells under spectra of blackbody (6000 K), air mass 0, air mass 1.5G, and air mass 1.5D, respectively. Moreover, detailed balance limits of tandem solar cells with perovskite top cells with bandgap range of 1.60–1.63 eV were realized with high conversion efficiency, when bandgap values of bottom cells are optimized in a range of 0.8–1.01 eV, and at 1.1 eV. It is also disclosed that the optical matching between top cell absorber and bottom cell absorber should be optimized for the high cell performances.

InGaN photocell significant efficiency enhancement on Si - an influence of interlayer physical properties

Nearly similar molar ratio of in and Ga in indium gallium nitride (InGaN) /Si photocells prefers to match InGaN conduction level energy to Si valance energy band for ohmic contact between two cells. At high temperature fabrication process, InGaN–Si interface shows highly defecting prone. Considering those tussles, InGaN-based/Si-based double-junction tandem solar cell was designed and fabricated. In₀.₄Ga₀.₆ N cell was fabricated on Si photocell by implementing AlN/SiO₂/Si₃N4 interlayers. Interlayer influence on quantum efficiency of InGaN cell was studied under ideal irradiance AM1.5 solar spectrum at 300°K. Because of insertion of interlayers between InGaN and Si; the gradual efficiency enhancement with respect to the overlayer h-GaN (a = 3.183 nm) plane lattice was found to 8.3%, 5.9% and 5.1% for AlN (a = 3.11 nm), for SiO₂ (a = 4.9 nm) and for Si₃N4 (a = 7.76 nm), respectively. AlN was found to be an excellent and SiO₂ as preferable interlayer compared with Si₃N4. Coherence (in-plane lattice matching) of nano-interlayer appears to reduce photonic electro-migration hurdle between InGaN and Si; therefore, progressive enrichment of efficiency was realized.

Investigation of InGaN/Si double junction tandem solar cells

In this work, the solar power conversion efficiency of InGaN/Si double junction tandem solar cells was investigated under 1-sun AM1.5 illumination, using realistic material parameters. With this intention, the current-voltage curves are calculated for different front recombination velocities and the influence of the bottom cell thickness on efficiency has been studied. The results show that a front recombination velocity value of 1e 3 cm/s is most advantageous and the use of relatively thick bottom cell is necessary to obtain conversion efficiency greater than 27%, at 300°k cell temperature. This efficiency will decrease as the operating temperature increase. Keywords: Photovoltaic, Efficiency, Carrier lifetimes, Recombination velocity, Temperature.

Structural dependences of localization and recombination of photogenerated carriers in the top GaInP Subcells of GaInP/GaAs double-junction tandem solar cells.

In high-efficiency GaInP/GaAs double-junction tandem solar cells, GaInP layers play a central role in determining the performance of the solar cells. Therefore, gaining a deeper understanding of the optoelectronic processes in GaInP layers is crucial for improving the energy conversion efficiency of GaInP-based photovoltaic devices. In this work, we firmly show strong dependences of localization and recombination of photogenerated carriers in the top GaInP subcells in the GaInP/GaAs double-junction tandem solar cells on the substrate misorientation angle with excitation intensity- and temperature-dependent photoluminescence (PL). The entire solar cell structures including GaInP layers were grown with metalorganic chemical vapor deposition on GaAs substrates with misorientation angles of 2° (denoted as Sample 2°) and 7° (Sample 7°) off (100) toward (111)B. The PL spectral features of the two top GaInP subcells, as well as their excitation-power and temperature dependences exhibit remarkable variation on the misorientation angle. In Sample 2°, the dominant localization mechanism and luminescence channels are due to the energy potential minima caused by highly ordered atomic domains; In Sample 7°, the main localization and radiative recombination of photogenerated carriers occur in the atomically disordered regions. Our results reveal a more precise picture on the localization and recombination mechanisms of photogenerated carriers in the top GaInP subcells, which could be the crucial factors in controlling the optoelectronic efficiency of the GaInP-based multijunction photovoltaic devices.

Super transverse diffusion of minority carriers in GaxIn1−xP/GaAs double-junction tandem solar cells

In this work, remarkable transverse diffusion of minority carriers in the GaxIn1−xP top subcell of a GaxIn1−xP/GaAs double-junction tandem solar cell is revealed by the electroluminescence (EL) image surveying. As the forward bias is increased, the overall EL intensity rapidly increases, but the topographical distribution of lateral intensity becomes more uneven. By analyzing the relation between the measured EL emission intensity and diffusion parameters of electrically injected minority carriers, the transverse diffusion length of the minority carriers is determined to be ∼93μm at the forward bias of 2.75V, which is 30 times larger than that of unbiased GaxIn1−xP single layer. Possible influence of such super diffusion of charge carriers on the conversion efficiency of tandem solar cells is discussed.

Impact of sub-cell internal luminescence yields on energy conversion efficiencies of tandem solar cells: A design principle

To develop a realistic design principle, we calculated the maximum conversion efficiency ηsc and optimized sub-cell band-gap energies Eg in double-junction tandem solar cells via a detailed-balance theory, paying particular attention to their dependence on internal luminescence quantum yields yint of the top and bottom sub-cell materials. A strong drop in the maximum ηsc occurs when yint slightly drops from 1 to 0.9, where the drop in yint of the bottom cell causes a stronger effect than that of the top cell. For low values of yint, the maximum ηsc has a simple logarithmic dependence on the geometric mean of the two sub-cells'yint.

Solution-processed small-molecule solar cells: breaking the 10% power conversion efficiency

A two-dimensional conjugated small molecule (SMPV1) was designed and synthesized for high performance solution-processed organic solar cells. This study explores the photovoltaic properties of this molecule as a donor, with a fullerene derivative as an acceptor, using solution processing in single junction and double junction tandem solar cells. The single junction solar cells based on SMPV1 exhibited a certified power conversion efficiency of 8.02% under AM 1.5 G irradiation (100 mW cm−2). A homo-tandem solar cell based on SMPV1 was constructed with a novel interlayer (or tunnel junction) consisting of bilayer conjugated polyelectrolyte, demonstrating an unprecedented PCE of 10.1%. These results strongly suggest solution-processed small molecular materials are excellent candidates for organic solar cells.

Surexpression de l’IL-31 dans une forme sporadique de lichen amyloïde : un lien avec le prurit ?

Radiative recombination of carriers in two kinds of GaxIn1−xP/GaAs double-junction tandem solar cell structures was investigated by using room-temperature electroluminescence (EL) and photoluminescence (PL) techniques. Efficient radiative recombination was observed simultaneously in the top and the bottom subcells in both the samples. By studying the behavior of EL and PL spectra, the radiative recombination intensity ΦEL was demonstrated to be reliant on the material-dependent radiative recombination coefficient, base layer doping concentration and thickness. Furthermore, dependence of ΦEL on substrate misorientation in both the subcells was also evidenced, which was explained in terms of the growth-induced variations in microstructure for the GaInP top cell and in potential barrier profile across the p–n junction for the GaAs bottom cell. Based on these observations, the radiative recombination in the two base layers of the subcells was demonstrated to be the major carrier loss mechanism in the GaxIn1−xP/GaAs double-junction tandem photovoltaic devices and should be suppressed.

Radiative recombination of carriers in the GaxIn1−xP/GaAs double-junction tandem solar cells

Radiative recombination of carriers in two kinds of GaxIn1−xP/GaAs double-junction tandem solar cell structures was investigated by using room-temperature electroluminescence (EL) and photoluminescence (PL) techniques. Efficient radiative recombination was observed simultaneously in the top and the bottom subcells in both the samples. By studying the behavior of EL and PL spectra, the radiative recombination intensity ΦEL was demonstrated to be reliant on the material-dependent radiative recombination coefficient, base layer doping concentration and thickness. Furthermore, dependence of ΦEL on substrate misorientation in both the subcells was also evidenced, which was explained in terms of the growth-induced variations in microstructure for the GaInP top cell and in potential barrier profile across the p–n junction for the GaAs bottom cell. Based on these observations, the radiative recombination in the two base layers of the subcells was demonstrated to be the major carrier loss mechanism in the GaxIn1−xP/GaAs double-junction tandem photovoltaic devices and should be suppressed.

Thin film solar cells incorporating microcrystalline Si1–xGex as efficient infrared absorber: an application to double junction tandem solar cells

AbstractWe have fabricated efficient (∼7–8%) hydrogenated microcrystalline Si1–xGex (µc‐Si1–xGex:H, x ∼ 0.1–0.17) single junction p‐i‐n solar cells with markedly higher short‐circuit current densities than for µc‐Si:H (x = 0) solar cells due to enhanced infrared absorption. By replacing the conventional µc‐Si:H with the µc‐Si1–xGex:H as infrared absorber in double junction tandem solar cells, the bottom cell thickness can be reduced by more than half while preserving the current matching with hydrogenated amorphous silicon (a‐Si:H) top cell. An initial efficiency of 11.2% is obtained for a‐Si:H/µc‐Si0.9Ge0.1:H solar cell with bottom cell thickness less than 1 µm. Copyright © 2009 John Wiley & Sons, Ltd.