Si Tandem Solar Cells Research Articles

Stable pure-iodide wide-band-gap perovskites for efficient Si tandem cells via kinetically controlled phase evolution

<h2>Summary</h2> Halide perovskites, promising top-cell materials for efficient Si tandem solar cells, suffer from halide segregation, which results from the halide mixing necessary for achieving band-gap widening. We report pure-iodide wide-band-gap perovskite top cells that are fundamentally free of halide segregation. Cs and dimethylammonium cations were incorporated simultaneously into the A-site of perovskite structure to increase the band gap while maintaining the tolerance factor. However, the incorporation of dual cations resulted in the simultaneous formation of orthorhombic and hexagonal secondary phases rather than forming the pure perovskite phase, owing to the different precipitation kinetics between cations. We demonstrated that this strategy can only be implemented by the phase-controlled nucleation of the Cs-rich composition that governs the desired phase evolution. The pure-iodide perovskite top cell exhibited excellent photo-stability (1% degradation after 1,000 h of continuous operation; ISOS-L-1I, white LED), and its Si tandem exhibited a high conversion efficiency of 29.4% (28.37% certified).

Correlation between detailed balance limit and actual environmental factors for perovskite/crystalline Si tandem solar cells with different structures

Detailed balance limits are estimated in perovskite/Si tandem solar cells with two-terminal (2T), four-terminal (4T), and series parallel tandem (SPT) configurations based on various environmental factors (average photon energy (APE), irradiance (Irr), and module temperature (Tmod)) in a year with data point numbers of 201,139. Bottom bandgap (Eg-bottom) of Si bottom subcell is fixed at 1.12 eV. Contour maps of conversion efficiency (η) as functions of top bandgap (Eg-top) and environmental factors are consequently disclosed. Eg-top is optimized under standard test conditions at 1.73 eV for 2T, 1.82 eV for 4T, and 1.83 eV for SPT. These optimized Eg-top values are not varied under variations of Irr and Tmod. Furthermore, η under increased APE is enhanced with enhanced optimized Eg-top proper for blue-rich spectrum. Ultimately, the contour maps of η as functions of Eg-top and APE are beneficial for selections of proper Eg-top of the tandem solar cells for maximized η, when actual outdoor APE is known.

Estimation of annual energy generation of perovskite/crystalline Si tandem solar cells with different configurations in central part of Japan

Detailed balance limit of perovskite/Si tandem solar cells with two-terminal (2T), four-terminal (4T), and series parallel tandem (SPT) configurations was calculated under a constant bandgap (Eg-bottom) of 1.12 eV of Si bottom subcells. Performances in the 2T configuration are most influenced by the Eg-top, because Eg-top can result in current mismatching if Eg-top is not appropriate. The ideal Eg-top values are 1.73 eV for 2T, 1.82 eV for 4T, and 1.83 eV for SPT under standard AM1.5G spectrum. Consequently, with the ideal Eg-top values, the highest possible efficiency (η) values are 44.8% for 2T, 45.0% for 4T and 44.7% for SPT. Furthermore, detailed balance limit under actual outdoor environmental factors at Shiga-prefecture in Japan was scrutinized. It is found that the outdoor spectral variation has the significant impact on the efficiency limit especially in a case of 2T. Also, the outdoor solar spectra at this observed outdoor location mostly are the blue-rich spectra over a year. As a result, the perovskite/Si tandem solar cell with the large ideal Eg-top of 1.82 eV in 4T configuration is the most appropriate to generate the possible highest η, thereby resulting in the highest annual energy generation.

Device simulation of quasi-two-dimensional perovskite/silicon tandem solar cells towards 30%-efficiency

Perovskite/silicon (Si) tandem solar cells have been recognized as the next-generation photovoltaic technology with efficiency over 30% and low cost. However, the intrinsic instability of traditional three-dimensional (3D) hybrid perovskite seriously hinders the lifetimes of tandem devices. In this work, the quasi-two-dimensional (2D) (BA)2(MA) n – 1Pb n I3n + 1 (n = 1, 2, 3, 4, 5) (where MA denotes methylammonium and BA represents butylammonium), with senior stability and wider bandgap, are first used as an absorber of semitransparent top perovskite solar cells (PSCs) to construct a four-terminal (4T) tandem devices with a bottom Si-heterojunction cell. The device model is established by Silvaco Atlas based on experimental parameters. Simulation results show that in the optimized tandem device, the top cell (n = 4) obtains a power conversion efficiency (PCE) of 17.39% and the Si bottom cell shows a PCE of 11.44%, thus an overall PCE of 28.83%. Furthermore, by introducing a 90-nm lithium fluoride (LiF) anti-reflection layer to reduce the surface reflection loss, the current density (J sc) of the top cell is enhanced from 15.56 mA/cm2 to 17.09 mA/cm2, the corresponding PCE reaches 19.05%, and the tandem PCE increases to 30.58%. Simultaneously, in the cases of n = 3, 4, and 5, all the tandem PCEs exceed the limiting theoretical efficiency of Si cells. Therefore, the 4T quasi-2D perovskite/Si devices provide a more cost-effective tandem strategy and long-term stability solutions.

Scalable Growth of Stable Wide‐Bandgap Perovskite towards Large‐Scale Tandem Photovoltaics

Upscaling and stabilizing efficient wide‐bandgap perovskite solar cells (PSCs) are critical for the commercialization of tandem photovoltaics. Herein, solvent engineering is applied for scalable deposition of wide‐bandgap (≈1.72 eV) perovskite by the introduction of N‐methyl‐2‐pyrrolidone (NMP) additives, which enables compact and phase‐stable FA0.83Cs0.17Pb(I0.7Br0.3)3 perovskite even without the use of antisolvent. By further passivation with a 2‐thiophenemethylammonium bromide (2‐ThMABr)‐based quasi‐2D perovskite (n = 2) on the surface of 3D perovskite, a champion power conversion efficiency (PCE) of 19.46% with a higher open‐circuit voltage of 1.219 V for a small‐sized wide‐bandgap PSC is achieved. It also exhibits excellent long‐term stability, maintaining 93% of its initial PCE after 2000 h storage in the air without encapsulation. In addition, this wide‐bandgap perovskite is also easy to be upscaled via a blade‐coating strategy, which demonstrates high PCEs of 16.07% and 13.03% with active areas of 46.5 and 123.0 cm2, respectively. Furthermore, the application of this wide‐bandgap perovskite for four‐terminal (4‐T) perovskite/silicon (Si) tandem solar cells also demonstrates high PCEs of 23.85% and 19.51% with active areas of 0.16 and 1.0 cm2. The work demonstrates a great potential toward large‐area efficient and stable wide‐bandgap PSCs and perovskite/Si tandem cells.

Loss Analysis of High-Efficiency Perovskite/Si Tandem Solar Cells for Large Market Applications

The Si tandem solar cells composes of III-V, II-VI, chalcogenide and perovskite top cells and Si bottom cells are very attractive for creation of new markets. The perovskite/Si tandem solar cells are thought to be one of the most promising PV devices because of high-efficiency and low-cost potential. However, efficiencies of perovskite/Si tandem solar cells with an efficiency of 29.8% are lower compared to 39.5% with III-V 3-junction tandem solar cells and 35.9% with III-V/Si 3-junction tandem solar cells. Therefore, it is necessary to clarify and reduce several losses of perovskite/Si tandem solar cells. This paper presents high efficiency potential of perovskite/Si tandem solar cells analyzed by using our analytical procedure and discusses about non-radiative recombination, optical and resistance losses in those tandem solar cells. The perovskite/Si 2-junction tandem solar cells is shown to have efficiency potential of 37.4% as a result of non-radiative recombination loss of 2.3%, optical loss of 2.7% and resistance loss of 3.1%. Although the perovskite/Si 3-junction tandem solar cells are thought to be very attractive because of higher efficiency with an efficiency of more than 42%, decreasing non-radiative recombination loss in wide bandgap perovskite solar cell materials is pointed out to be necessary.

Low‐Cost Strategy for High‐Efficiency Bifacial Perovskite/c‐Si Tandem Solar Cells

Many studies have confirmed that the perovskite/crystalline silicon (c‐Si) tandem solar cells (TSCs) can achieve excellent photovoltaic performance far exceeding that of single‐junction solar cells. However, the quite thick c‐Si bottom‐cells have to be used to fully absorb near‐infrared photons, which greatly improves the cost of the TSCs. The bifacial two‐terminal TSCs not only can improve the energy output by introducing rear incident light, but also significantly reduce the Si thickness while maintaining high efficiency. Herein, the photovoltaic performance of bifacial perovskite/c‐Si TSCs under different Si thicknesses, pyramid heights, and albedos have been calculated. It is found that the thickness of the c‐Si sub‐cells can be reduced from the current 250 to 25 μm, and only the albedos need to be increased by 18.6% to cover the absorption loss in the near‐infrared. It is recommended that 100‐μm thick c‐Si is a suitable candidate and optimized the size of the Si pyramids (1.0 μm) to obtain excellent light trapping performance. This work can serve as a guidance for experimental preparation of low‐cost and high‐efficiency bifacial perovskite/c‐Si TSCs.

Si tunnel junctions obtained by proximity rapid thermal diffusion for tandem photovoltaic cells

Low-resistance c-Si Esaki tunnel junctions (TJ) can be applied in two-terminal Si-based tandem solar cells to electrically connect two sub-cells. Proximity rapid thermal diffusion (PRTD) is an economical and facile method to fabricate the Si tunnel junctions with a damage-free surface. The p++/n++ Si TJ on (111)-oriented c-Si wafer produced by combining PRTD and photovoltaic industrial techniques is reported in this work. The adjustment of the n++ emitter by a two-step rapid thermal annealing effectively facilitates the realization of the p++/n++ TJ. The peak current density of a tunnel diode based on this TJ is within the range 140–192 A cm−2 with a peak to valley current ratio of 1.9–3.2. Such a p++/n++ TJ is implemented in III–V nanowires (NWs) on Si tandem solar cells. Despite the defectuosity of the NWs array, we demonstrate that an increase of the open-circuit voltage is observed compared with the sole single-junction Si solar cell. This kind of TJ can also be integrated with other top cell materials such as perovskites and copper indium gallium selenide. Low-cost and high-efficiency c-Si based tandem solar cells might be produced with the application of Si TJs obtained by PRTD.

Metamorphic Tunnel Junctions Grown Via MOCVD Designed for GaAs0.75P0.25/Si Tandem Solar Cells

A high-performance metamorphic Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> /GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> heterojunction tunnel junction structure was developed for application to monolithic epitaxial GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> /Si 1.7 eV/1.1 eV bandgap tandem solar cells produced via metal-organic chemical vapor deposition. Doping optimization focused on both bulk doping concentrations and mitigating the transient incorporation effects that otherwise causes nonabrupt doping profiles in the Te doped layer. These efforts resulted in a fully relaxed metamorphic tunnel diode at the target lattice constant having a peak tunneling current density (JP) of 279.1 A·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and a zero-bias resistance-area product (RA) of 3.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . After postgrowth annealing to emulate the thermal load of the GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> top cell growth and elimination of the performance-enhancing carbon activation anneal, the device achieved JP = 13.1 A·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and RA = 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . These worst-case values are very promising as they enable the operation of GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> /Si tandems under one-sun AM1.5G illumination with negligible series resistance and at AM1.5D concentrations up to 240 suns with only 0.1% absolute efficiency loss.

Low-temperature direct growth for low dislocation density in III-V on Si towards high-efficiency III-V/Si tandem solar cells

Si tandem solar cells are attractive for new applications such as photovoltaic-powered vehicles because of their high-efficiency and low-cost potential. In particular, III-V/Si tandem solar cells have higher efficiency potential compared to perovskite/Si and other Si tandem solar cells. Although the direct growth of III-V layers on Si is very attractive for cost reduction and simple processing potential, high-quality growth of the III-V thin-film layer on Si is necessary. The paper discusses the effectiveness of the low-temperature growth of III-V layer on Si substrates for realizing low-density dislocations on Si substrates. Low dislocation density of less than 3 × 105 cm−2 in GaAs-on-Si by low-temperature growth is demonstrated in this study. According to our analytical results, this low dislocation density shows high potential efficiency of more than 33% and 38% for III-V/Si 2-junction and 3-junction tandem solar cells, respectively.

Improved design of InGaP/GaAs//Si tandem solar cells

Optimizing any tandem solar cells design before making them experimentally is an important way of reducing development costs. Hence, in this work, we have used a complete analytical model that includes the important effects in the depletion regions of the III-V compound cells in order to simulate the behavior of two and four-terminal InGaP/GaAs//Si tandem solar cells for optimizing them. The design optimization procedure is described first, and then it is shown that the expected practical efficiencies at 1 sun (AM1.5 spectrum) for both two and four-terminal tandem cells can be around 40% when the appropriate thickness for each layer is used. The optimized design for both structures includes a double MgF2/ZnS anti-reflection layer (ARC). The results show that the optimum thicknesses are 130 (MgF2) and 60 nm (ZnS), respectively, while the optimum InGaP thickness is 220 nm and GaAs optimum thickness is 1800 nm for the four-terminal tandem on a HIT silicon solar cell (with total tandem efficiency around 39.8%). These results can be compared with the recent record experimental efficiency around 35.9% for this kind of solar cells. Therefore, triple junction InGaP/GaAs//Silicon tandem solar cells continue being very attractive for further development, using high efficiency HIT silicon cell as the bottom sub-cell.

Designing an Epitaxially-Integrated DBR for Dislocation Mitigation in Monolithic GaAsP/Si Tandem Solar Cells

This work explores epitaxially integrated distributed Bragg reflectors (DBR) as a strategy to mitigate the impact of threading dislocations on the performance of monolithic GaAs0.75P0.25/Si tandem solar cells. The constraints present because of materials availability and the optical transmission profile of the GaAs0.75P0.25 top cell require the use of an enhanced bandwidth DBR design achieved by combining two narrow-band DBRs with different central wavelengths. The impact of this DBR structure on J SC, along with the competing effects of threading dislocation density (TDD), is investigated using a robust, experimentally informed analytical model. Implementing this DBR within the GaAs0.75P0.25/Si tandem cell structure is predicted to yield a short-circuit current enhancement equivalent to the ∼1.8× reduction in TDD, providing a clear demonstration of its promise as a design methodology for mitigating the impact of non-negligible defect populations.

Surface Engineering of Ambient-Air-Processed Cesium Lead Triiodide Layers for Efficient Solar Cells

<h2>Summary</h2> Cesium lead triiodide (CsPbI₃) presents a desirable band gap, does not require the use of mixed halides for Si tandem solar cells, and possesses relatively high thermal stability owing to its inorganic components. However, the power conversion efficiency (PCE) of CsPbI₃ is lower than that of organic cation-based halide perovskites with identical band gaps. The main factors that govern the PCE of CsPbI₃ are the surface morphology and defect passivation of its thin films on substrates. In this study, we used the sequential dripping of a methylammonium chloride (MACl) solution (SDMS) to obtain highly uniform and pinhole-minimized thin films by controlling the intermediate stages of the crystallization process, followed by surface passivation using octylammonium iodides in ambient air. SDMS accelerated the crystallization process of the CsPbI₃ perovskite layer, resulting in the formation of a uniform and dense surface with few pinholes. Consequently, we fabricated CsPbI₃ solar cells with excellent PCE (20.37%).

Pathways and Potentials for III–V on Si Tandem Solar Cells Realized Using a ZnO-Based Transparent Conductive Adhesive

This work presents a new type of transparent conductive adhesive and its electrical and optical properties with regards to an application in III–V on Silicon tandem solar cells. The developed adhesive is based on a doped ZnO and deposited by spray coating. The optical interconnection of the two sub-cells is identified as one of the major challenges due to the reflectance at the bond and possible approaches to reduce the reflectance are investigated by optical simulations. Regarding the electrical interconnection, an ITO-based contact layer reduced the lowest measured connecting resistivity from previously 17 Ω·cm² [1] down to 0.12 Ω·cm². It is shown that the homogeneity of the bond correlates with its conductivity and can be improved by adjusting the glueing process according to the calcination process of the adhesive. Taking both the electrical and optical parameters of the transparent conductive adhesive into account, the efficiency of a triple junction solar cell was estimated.

Size-Dependent and Enhanced Photovoltaic Performance of Solar Cells Based on Si Quantum Dots

Recently, extensive studies have focused on exploring a variety of silicon (Si) nanostructures among which Si quantum dots (Si QDs) may be applied in all Si tandem solar cells (TSCs) for the time to come. By virtue of its size tunability, the optical bandgap of Si QDs is capable of matching solar spectra in a broad range and thus improving spectral response. In the present work, size-controllable Si QDs are successfully obtained through the formation of Si QDs/SiC multilayers (MLs). According to the optical absorption measurement, the bandgap of Si QDs/SiC MLs shows a red shift to the region of long wavelength when the size of dots increases, well conforming to quantum confinement effect (QCE). Additionally, heterojunction solar cells (HSCs) based on Si QDs/SiC MLs of various sizes are presented and studied, which demonstrates the strong dependence of photovoltaic performance on the size of Si QDs. The measurement of external quantum efficiency (EQE) reveals the contribution of Si QDs to the response and absorption in the ultraviolet–visible (UV-Vis) light range. Furthermore, Si QDs/SiC MLs-based solar cell shows the best power conversion efficiency (PCE) of 10.15% by using nano-patterned Si light trapping substrates.

Experimental Determination of Complex Optical Constants of Air‐Stable Inorganic CsPbI3 Perovskite Thin Films

Air‐stable inorganic cesium lead iodide (CsPbI3) perovskite thin films with a bandgap of 1.7 eV are a promising candidate for tandem cell solar cells, comprising a perovskite top cell with a crystalline silicon bottom cell. The device design and simulations are important to develop high‐efficiency photovoltaic devices. However, knowledge of complex optical constants of the CsPbI3 thin films is mandatory to complement such tasks. Herein, air‐stable inorganic CsPbI3 perovskite thin films are prepared using one‐step synthesis through a spin‐coating method. Variable angle spectroscopic ellipsometry (VASE) is then conducted at five angles (43.9°, 48.9°, 53.9°, 58.9°, and 63.9°) to obtain ellipsometric data (Ψ and Δ). The thickness nonuniformity model of the perovskite thin film combined with an effective medium approximation for describing rough surface is adopted to achieve excellent fitting. The complex optical constants of the CsPbI3 thin film are experimentally obtained in the wavelength range of 300–1200 nm. The present results open the door for design and simulations on high‐efficiency CsPbI3/c‐Si tandem solar cells.

Heteroepitaxy of GaAsP and GaP on GaAs and Si by low pressure hydride vapor phase epitaxy

Direct heteroepitaxy of GaAsP and GaP on GaAs and on Si by low-pressure hydride vapor phase epitaxy (HVPE) is investigated as prior studies for photovoltaics and non-linear optics applications. When growing GaAsP on GaAs, it is found that the ambient gas during substrate pre-heating influences the ternary composition as well as the crystalline quality of the subsequent growth. GaAs0.72P0.28 with bandgap energy of 1.76 eV has been achieved, which would be suitable for a top cell in Si tandem solar cell structures. Growth of GaP was investigated on planar GaAs as a prior study for realizing orientation patterned (OP) GaP on OP-GaAs. Threading dislocations caused by the 3.6% lattice mismatch between GaP and GaAs are suppressed by adjusting the GaCl flow, achieving a low full width at half maximum of 146 arcsec for the X-ray diffraction omega scan. Direct heteroepitaxy of GaAsP on Si aiming for achieving a GaAsP/Si dual junction solar cell is demonstrated. The inherent problem of initiating nucleation during the direct heteroepitaxy of III-V on Si by HVPE is overcome by utilizing the vapor mixing approach to grow a low-temperature GaP buffer layer on Si, followed by a GaAsP layer grown by conventional HVPE.

Simulation analysis of a high efficiency GaInP/Si multijunction solar cell

The solar power conversion efficiency of a gallium indium phosphide (GaInP)/silicon (Si) tandem solar cell has been investigated by means of a physical device simulator considering both mechanically stacked and monolithic structures. In particular, to interconnect the bottom and top sub-cells of the monolithic tandem, a gallium arsenide (GaAs)-based tunnel-junction, i.e. GaAs(n+)/GaAs(p+), which assures a low electrical resistance and an optically low-loss connection, has been considered. The J–V characteristics of the single junction cells, monolithic tandem, and mechanically stacked structure have been calculated extracting the main photovoltaic parameters. An analysis of the tunnel-junction behaviour has been also developed. The mechanically stacked cell achieves an efficiency of 24.27% whereas the monolithic tandem reaches an efficiency of 31.11% under AM1.5 spectral conditions. External quantum efficiency simulations have evaluated the useful wavelength range. The results and discussion could be helpful in designing high efficiency monolithic multijunction GaInP/Si solar cells involving a thin GaAs(n+)/GaAs(p+) tunnel junction.

Overview of Si Tandem Solar Cells and Approaches to PV-Powered Vehicle Applications

ABSTRACTDevelopment of high-efficiency solar cell modules and new application fields are significant for the further development of photovoltaics (PV) and creation of new clean energy infrastructure based on PV. Especially, development of PV-powered EV applications is desirable and very important for this end. This paper shows analytical results for efficiency potential of various solar cells for choosing candidates of high-efficiency solar cell modules for automobile applications. As a result of analysis, Si tandem solar cells are thought to be some of their candidates. This paper also overviews efficiency potential and recent activities of various Si tandem solar cells such as III-V/Si, II-VI/Si, chalcopyrite/Si, perovskite/Si and nanowire/Si tandem solar cells. The III-V/Si tandem solar cells are expected to have a high potential for various applications because of high efficiency with efficiencies of more than 36% for 2-junction and 42 % for 3-junction tandem solar cells under 1-sun AM1.5 G, lightweight and low-cost potential. Recent results for our 28.2 % efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si 3-junction solar cell are also presented. Approaches to automobile application by using III-V/Si tandem solar cells and static low concentration are presented.

Role of PV-Powered Vehicles in Low-Carbon Society and Some Approaches of High-Efficiency Solar Cell Modules for Cars

Development of highly-efficient photovoltaic (PV) modules and expanding its application fields are significant for the further development of PV technologies and realization of innovative green energy infrastructure based on PV. Especially, development of solar-powered vehicles as a new application is highly desired and very important for this end. This paper presents the impact of PV cell/module conversion efficiency on reduction in CO2 emission and increase in driving range of the electric based vehicles. Our studies show that the utilization of a highly-efficient (higher than 30%) PV module enables the solar-powered vehicle to drive 30 km/day without charging in the case of light weight cars with electric mileage of 17 km/kWh under solar irradiation of 3.7 kWh/m2/day, which means that the majority of the family cars in Japan can run only by the sunlight without supplying fossil fuels. Thus, it is essential to develop high-efficiency as well as low-cost solar cells and modules for automotive applications. The analytical results developed by the authors for conversion efficiency potential of various solar cells for choosing candidates of the PV modules for automotive applications are shown. Then we overview the conversion efficiency potential and recent progress of various Si tandem solar cells, such as III-V/Si, II-VI/Si, chalcopyrite/Si, and perovskite/Si tandem solar cells. The III-V/Si tandem solar cells are expected to have a high potential for various applications because of its high conversion efficiency of larger than 36% for dual-junction and 42% for triple-junction solar cells under 1-sun AM1.5 G illumination, lightweight and low-cost potentials. The analysis shows that III-V based multi-junction and Si based tandem solar cells are considered to be promising candidates for the automotive application. Finally, we report recent results for our 28.2% efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si triple-junction solar cell. In addition, new approaches which are suitable for automotive applications by using III-V triple-junction, and static low concentrator PV modules are also presented.