Top Solar Cell Research Articles

Finding junction partners for CsPbI3 in a two-terminal tandem solar cell: A theoretical prospect

Abstract Screening ideal partner materials for the CsPbI3 perovskite is crucial for developing all-inorganic perovskite-based tandem solar cells. Here, we quantize the performance of all-inorganic tandem solar cells combining the CsPbI3 perovskite with c-Si, GaAs, CdTe, CIGS, and CsSnI3, by analyzing the measured spectral efficiencies and developing macroscopic continuum device (MCD) model. Firstly, we integrate the MCD model and the principles of detailed balance (Shockley-Queisser limit model, SQM) to investigate the top CsPbI3 solar cell with varying thickness and the rear sub-cell with different bandgaps. Without considering the nonradiative recombination and absorptivity in the rear sub-cell, an efficiency of over 32% can be reached by selecting the low bandgap materials (Egap ~ 1.1 eV) as the rear sub-cell. Furthermore, after the simulation by MCD model that takes the charge recombination, absorptivity and optimal thicknesses for both sub-cells in tandem architectures into account, CIGS is found to be one of the best junction partners for CsPbI3. During the simulations, a unique bisection search algorithm is used to guarantee that the continuity of electric potential near the junction layer and the current matching of sub-cells in the tandem solar cells. As a result, a CsPbI3(470 nm)/CIGS(2000 nm) tandem solar cell with the best-modeled efficiency of 24.40% can be achieved, which is affirmed by a recent experimental result. Finally, we simulate the corresponding bifacial tandem photovoltaic device, and the optimal modeled efficiency can be further enhanced to 25.58%.

Synergistic Tandem Solar Electricity-Water Generators

Summary Energy and clean water are two intertwined fundamental elements for human civilization and sustainable development. Here, we devise a monolithic tandem solar electricity-water generator that synergistically produces electricity and clean water by utilizing the full spectrum of solar irradiance. The tandem generator has two components: a top infrared-transparent photovoltaic device using above-band-gap photons, and a bottom solar water purifier using the below-band-gap photons. More strikingly, a well-designed water-proof thermal interconnecting layer (WTIL) makes these two components work synergistically: the bottom purifier serves as an evaporative cooler of the top solar cell to increase its efficiency, whereas the thermalization energy of the top cell is reutilized by the bottom purifier for producing more clean water. We experimentally demonstrate that a prototype hybrid tandem solar device with WTIL can generate electricity with a power output of 204 W m−2 and purify water at a rate of 0.80 kg m−2 h−1 under 1-sun illumination.

Energy yield of bifacial textured perovskite/silicon tandem photovoltaic modules

Bifacial perovskite/crystalline silicon (c-Si) tandem photovoltaic (PV) modules that harvest albedo radiation are a promising strategy to further enhance the energy yield (EY) of monofacial perovskite/c-Si tandem PV modules. Given the required current matching in bifacial perovskite/c-Si two-terminal (2T) tandem PV modules, predicting the expected enhancement in EY requires an advanced EY modelling framework. In this study, the architecture, module tilt, perovskite absorber layer thickness, and bandgap of the perovskite top solar cell are optimized for several types of grounds and two locations. Compared to bifacial c-Si single-junction PV modules, the relative enhancement in EY of textured bifacial perovskite/c-Si 2T tandem PV modules is around 24–38% for an exemplary grass ground (mean albedo = 35%). With increasing albedo, the optimum bandgap of the perovskite top solar cell decreases from 1.72 eV (black ground, mean albedo = 0%) to 1.55 eV (snow, mean albedo = 88%). This is attributed to enhanced current generation only in the c-Si bottom solar cell due to albedo radiation, entering the solar cell at the rear side. In addition, minor optical losses due to ground shading are found for modules with a finite mounting height in the range of 1 m. Overall, our study highlights the importance of EY modelling to assess the performance of bifacial perovskite/c-Si tandem PV. It provides direction for the design of bifacial perovskite/c-Si tandem solar cells with regard to the device architecture and the choice of the perovskite material with regard to its bandgap.

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8MA0.2Sn0.5Pb0.5I3) for All‐Perovskite Tandem Solar Cells

AbstractAll‐perovskite multijunction photovoltaics, combining a wide‐bandgap (WBG) perovskite top solar cell (EG ≈1.6–1.8 eV) with a low‐bandgap (LBG) perovskite bottom solar cell (EG < 1.3 eV), promise power conversion efficiencies (PCEs) >33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum‐assisted growth control (VAGC) of solution‐processed LBG perovskite thin films based on mixed Sn–Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well‐established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge‐carrier lifetime. The improved optoelectronic characteristics enable high‐performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four‐terminal all‐perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active‐area solar cells up to 1 cm2.

Semi-Transparent Perovskite Solar Cells with ITO Directly Sputtered on Spiro-OMeTAD for Tandem Applications.

Perovskite silicon tandem solar cells have the potential to overcome the efficiency limit of single-junction solar cells. For both monolithic and mechanically stacked tandem devices, a semi-transparent perovskite top solar cell, including a transparent contact, is required. Usually, this contact consists of a metal oxide buffer layer and a sputtered transparent conductive oxide. In this work, semi-transparent perovskite solar cells in the regular n-i-p structure are presented with tin-doped indium oxide (ITO) directly sputtered on the hole conducting material Spiro-OMeTAD. ITO process parameters such as sputter power, temperature, and pressure in the chamber are systematically varied. While a low temperature of 50 °C is crucial for good device performance, a low sputter power has only a slight effect, and an increased chamber pressure has no influence on device performance. For the 5 × 5 mm2 perovskite cell with a planar front side, a 105 nm thick ITO layer with a sheet resistance of 44 Ω sq-1 allowing for the omission of grid fingers and a MgF2 antireflection coating are used to improve transmission into the solar cells. The best device achieved an efficiency of 14.8%, which would result in 24.2% in a four-terminal tandem configuration.

Toward scalable perovskite‐based multijunction solar modules

AbstractPerovskite‐based multijunction solar cells can potentially overcome the power conversion efficiency (PCE) limits of established solar cell technologies. The technology combines high‐efficiency perovskite top solar cells with crystalline silicon (c‐Si) and copper indium gallium diselenide (CIGS) single‐junction solar cells enabling a more efficient harnessing of solar energy. In this work, we present high‐efficiency and scalable perovskite‐CIGS and perovskite‐Si multijunction solar modules in a four‐terminal configuration. We design the multijunction solar modules for minimal optical losses through careful optical engineering. In addition to optimized light coupling, the solar modules are fabricated in a scalable device design. Starting from lab‐scale cells of 0.13 cm2, we scale up the multijunction devices by two orders of magnitude to 16 cm2 and investigate the various losses affecting the PCE of large‐area multijunction solar modules, thus providing valuable insights into scalability of the technology. The champion perovskite‐CIGS and perovskite‐Si multijunction solar modules exhibit higher PCE than the stand‐alone devices on sizes up 16 cm2, paving the way for high‐effiency perovskite‐based multijunction photovoltaics. This work brings to forth relevant upscaling aspects of perovskite‐based multijunction solar cell technology, which is a key milestone in the road to commercial feasibility of the perovskite‐based multijunction solar cell technology.

Enhanced Performance of Dye-Sensitized Solar Cells Using Perovskite/DSSCs Tandem Design

Tandem solar cells were developed for improved efficiency in connection with perovskite solar cells and dye-sensitized solar cells. The organic dye based on thioindigo and N719 were applied in fabricating dye-sensitized solar cells as photosensitizers. We achieved an 8.77% and 10.54% efficiency tandem solar cell formed by a top perovskite solar cell and dye-sensitized solar cells based on organic dye and N719 for the bottom cell, respectively. The photovoltage of tandem solar cells was reported about 1.1 V, but the photocurrent was limited by the dye-sensitized solar cells and was about 12.8 mAcm−2.

Vapor-Assisted Ex-Situ Doping of Carbon Nanotube toward Efficient and Stable Perovskite Solar Cells.

Single-walled carbon nanotubes (CNTs) has been considered as a promising material for a top electrode of perovskite solar cells owing to its hydrophobic nature, earth-abundance, and mechanical robustness. However, its poor conductivity, a shallow work function, and nonreflective nature have limited further enhancement in power conversion efficiency (PCE) of top CNT electrode-based perovskite solar cells. Here, we introduced a simple and scalable method to address these issues by utilizing an ex-situ vapor-assisted doping method. Trifluoromethanesulfonic acid (TFMS) vapor doping of the free-standing CNT sheet enabled tuning of conductivity and work function of the CNT electrode without damaging underneath layers. The sheet resistance of the CNT sheet was decreased by 21.3% with an increase in work function from 4.75 to 4.96 eV upon doping of TFMS. In addition, recently developed 2D perovskite-protected Cs-containing formamidium lead iodide (FACsPbI3) technology was employed to maximize the absorption. Because of the lowered resistance, better energy alignment, and improved absorption, the CNT electrode-based PSCs produced a PCE of 17.6% with a JSC of 24.21 mA/cm2, VOC of 1.005 V, and FF of 0.72. Furthermore, the resulting TFMS-doped CNT-PSCs demonstrated higher thermal and operational stability than bare CNT and metal electrode-based devices.

Performance Evaluation of Semitransparent Perovskite Solar Cells for Application in Four-Terminal Tandem Cells

The efficiency of perovskite-based tandem solar cells and the respective efficiency gain over the single-junction operation of the bottom cell strongly depend on the performance of the component cells. Thus, a fair comparison of reported top cells is difficult. We therefore compute the tandem cell efficiency for the combination of several semitransparent perovskite top solar cells and crystalline silicon or chalcopyrite bottom cells from the literature. We focus on four-terminal configurations but also estimate and discuss the differences between four- and two-terminal configurations. For each top cell, we thereby determine the tandem cell performance as a function of the bottom cell efficiency, which results in a linear relationship. From these data, we extract two parameters to quantify the suitability of the top cell: (i) the slope of the tandem vs. bottom cell efficiency, which is the effective transparency of the top cell, and (ii) the tandem cell efficiency for a targeted bottom cell. These two figu...

FTO-free top-illuminated colloidal quantum dot photovoltaics: Enhanced electro-optics in devices

A solar cell device architecture with top-illumination, where the light does not pass through the substrate, is advantageous for many applications. It is also specifically useful for the construction of tandem or multiple junction photovoltaic devices, with illumination through the top solar cell. Here, a top-illuminated colloidal quantum dot solar cell (TI-CQDSC) is demonstrated and compared with a conventional colloidal quantum dot solar cell (C-CQDSC) constructed on a FTO (fluorine doped tin oxide) glass substrate both theoretically and experimentally. The optical electric field distribution in the solar cells with different configuration is simulated using transfer matrix formalism and a more intense optical electric field was observed in TI-CQDSC, leading to a higher exciton generation rate within the colloidal quantum dot solid. The TI-CQDSCs are constructed on both nonconductive glass and flexible substrates, and a maximum power conversion efficiency of 6.4% and 5.6% is achieved, respectively, comparing to that of 5.9% for the C-CQDSC. The improved performance of the top illuminated solar cell is attributed to a combination of enhanced optical electric field intensity in the colloidal quantum dot solid and superior conductivity of the transparent metal film electrode.

Low band‐gap CuIn(S,Se)2 thin film solar cells using molecular ink with 9.5% efficiency (Phys. Status Solidi C 6/2017)

In order to achieve low band-gap thin film solar cells which can play an important role in tandem solar cells combined with perovskite top solar cells, the preparation of chalcopyrite absorbers is a major task. Wang et al. (article no. 1600169) report a non-vacuum simple solution coating approach for CuIn(S,Se)2 absorbers using an air stable molecular ink containing metal chlorides and thiourea in organic solvents. Careful balancing of ink concentration, number of precursor deposition cycles, and annealing temperature profile will transform the multilayer precursor into a sufficiently thick, continuous, large grained film as required for high quantum efficiency, and good red response of the cells. These optimizations aimed at high photo current have already led to an efficiency of 9.5% at a band-gap of 1.02 eV.

Top PV market solar cells 2016

Photovoltaic (PV) technologies which play a role in PV market are divided into basic two types: wafer-based (1st generation PV) and thin-film cell (2nd generation PV). To the first category belong mainly crystalline silicon (c-Si) cells (both mono- and multi-crystalline). In 2015 around 90% of the solar market belonged to crystalline silicon. To the 2nd generation solar cells belongs thin film amorphous silicon (a-Si) or a combination of amorphous and microcrystalline silicon (a-Si/μc-Si), compound semiconductor cadmium telluride (CdTe), compound semiconductor made of copper, indium, gallium and selenium (CIS or CIGS) and III–V materials. The PV market for thin film technology is dominated by CdTe and CIGS solar cells. Thin film solar cells’ share for all thin film technologies was only 10% in 2015. New emerging technologies, called 3rd generation solar cells, remain the subject of extensive R&D studies but have not been used in the PV market, so far. In this review the best laboratory 1st and 2nd generation solar cells that were recently achieved are described. The scheme of the layer structure and energy band diagrams will be analyzed in order to explain the boost of their efficiency with reference to the earlier standard designs.

Analysis of parasitic losses due to intermediate reflectors in silicon tandem solar cells

Intermediate reflecting layers (IRL) in multijunction solar cells improve the spectral light management and thereby increase the overall energy conversion efficiency. Nevertheless, the incorporation of an IRL can increase parasitic losses in the device mainly by three effects: (i) parasitic absorption in the IRL, (ii) increased parasitic absorption in the transparent front electrode due to the light reflection at the IRL, and (iii) reflection losses due to insufficient absorption of light in the top solar cell that is reflected at the IRL. Here, we investigate the different contributions of these three loss mechanisms on the external quantum efficiency and short-circuit current density by a combination of experiment and optical simulation. The parasitic absorption in the transparent front electrode is varied experimentally by a post-deposition laser annealing process on the front electrode layer. The experimental work is supplemented by rigorous optical simulations which allow to extract and vary the parasitic absorption losses in the IRL by a variation of the optical material properties. Furthermore, the cell reflectance is studied by experiment and simulation for different layer configurations. Our comparative study reveals that the dominating parasitic losses are absorption within the intermediate reflector and reflection out of the solar cell. From this study, we show one possible solution for advanced light management in tandem solar cells with intermediate reflectors.

Tandem Architecture of Perovskite and Cu(In,Ga)(S,Se)2 Created by Solution Processes for Solar Cells

Integrating tandem solar cell architectures into devices can improve their power conversion efficiency (PCE) by overcoming the limited incident light absorption range of a single absorber and reducing the thermalization loss. Here, fabricated tandem solar cells are successfully fabricated employing different absorber materials, in this case perovskite and Cu(In,Ga)(S,Se)2 (CIGS) as top and bottom cells, respectively. For cost effectiveness most tandem device manufacturing processes are achieved by solution‐based methods, which even provide the electrode layers. Using such a process to create a tandem device, a PCE of 8.34% for the semitransparent perovskite top solar cell and 2.48% for the CIGS bottom solar cell is obtained, resulting in an overall efficiency of 10.82% for the four‐terminal tandem device. This result highlights the potential of this solution‐based tandem configuration as a way to facilitate the creation of simple and inexpensive efficient light‐utilizing solar cell devices.

Ohmic-like contact formation at the rear interface between Cu(In,Ga)Se2 and ZnO:Al in a lift-off Cu(In,Ga)Se2 solar cell

A lift-off Cu(In,Ga)Se2 (CIGS) solar cell, which could serve as the top solar cell in a tandem-type solar cell, was fabricated with a superstrate-type structure consisting of soda-lime glass (SLG)/epoxy/Al/n-type ZnO:Al (AZO)/ZnO/CdS/p-type CIGS/n-type AZO (back electrode)/Al. This study proposes a method of realizing the ohmic-like contact between p-type CIGS and n-type AZO in a lift-off CIGS solar cell to improve the conversion efficiency (η). The sputtering conditions under which the n-type AZO layer was deposited, specifically the sample position and radio frequency (RF) power density, were optimized to form ohmic-like contact through trap-assisted tunneling recombination. The sputtering damage near the CIGS surface that induced the trap-assisted tunneling recombination was evaluated by examining the photoluminescence peak intensity. Ultimately, ohmic-like characteristics were attained for the p-type CIGS/n-type AZO interface under optimal AZO deposition conditions, with the sample positioned 0cm from the AZO target center and an RF power density of 2.4W/cm2. The proposed method was successfully applied to the fabrication of a lift-off CIGS solar cell. Consequently, an η value of 9.2% was obtained for the lift-off CIGS solar cell, which is 70% that of a substrate-type CIGS solar cell.

Increased Spectrum Utilization with GaAsP/SiGe Solar Cells Grown on Silicon Substrates

ABSTRACTWorld-record solar-to-electricity energy conversion efficiency has been previously achieved by photovoltaic devices that maximize the use of the solar spectrum, such as multi-junction tandem solar cells. These cells are made of III-V materials whose high cost is a strong limitation on their widespread commercial application. One solution to suppress the cost of these types of devices is to grow III-V solar cells on low-cost carrier materials such as silicon. We will discuss the material, structure and analysis of GaAsP/SiGe-on-silicon multi-junction tandem solar cells. A low threading dislocation density is realized by effective lattice-matching of the top and bottom cells which demonstrate a device that achieves high open-circuit voltage in the top solar cell. The GaAsP/SiGe solar cells have reached a measured efficiency of 20.6% under one sun concentration. Analysis of these results based on the product of the best parameters shows efficiency potential of 26% under one sun, 30.8% at 20× and 35.1% at 400×.

Investigation of Optical and Dielectric Constants of Organic-Inorganic CH3NH3PbI3 Perovskite Thin Films

CH3NH3PbI3 thin films with thicknesses in the region of 230-365 nm were prepared. The films were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD), ultraviolet-visible (UV-Vis) absorption and transmittance spectra. Based on the Kramers-Kronig relation and the transmittance spectra, the optical constants of the CH3NH3PbI3 thin films were investigated. Our results show that the absorption coefficient, extinction coefficient, refractive indices, real and imaginary components of the dielectric constant of the CH3NH3PbI3films are basically independent on the thicknesses of the films, which indicate our results are reliable. At 500 nm, above parameters of the films are ~1.38 × 105 cm-1, 0.55, 2.70, 7.01, and 3.13, respectively. The band gap is 1.595 eV. The refractive index of CH3NH3PbI3thin films is 2.84 at 633 nm, which imply that CH3NH3PbI3-based solar cells are ideal antireflection coatings for silicon solar cells (SCs) and are applicable to be top solar cell in monolithic silicon-based tandem solar cells for beyond the efficiency limit of Si SCs. Our results are meaningful for designing optoelectronic devices related to the perovskite thin-films.

Tandem Solar Cells Using GaAs Nanowires on Si: Design, Fabrication, and Observation of Voltage Addition

Multijunction solar cells provide us a viable approach to achieve efficiencies higher than the Shockley-Queisser limit. Due to their unique optical, electrical, and crystallographic features, semiconductor nanowires are good candidates to achieve monolithic integration of solar cell materials that are not lattice-matched. Here, we report the first realization of nanowire-on-Si tandem cells with the observation of voltage addition of the GaAs nanowire top cell and the Si bottom cell with an open circuit voltage of 0.956 V and an efficiency of 11.4%. Our simulation showed that the current-matching condition plays an important role in the overall efficiency. Furthermore, we characterized GaAs nanowire arrays grown on lattice-mismatched Si substrates and estimated the carrier density using photoluminescence. A low-resistance connecting junction was obtained using n(+)-GaAs/p(+)-Si heterojunction. Finally, we demonstrated tandem solar cells based on top GaAs nanowire array solar cells grown on bottom planar Si solar cells. The reported nanowire-on-Si tandem cell opens up great opportunities for high-efficiency, low-cost multijunction solar cells.

Material and Device Improvement of GaAsP Top Solar Cells for GaAsP/SiGe Tandem Solar Cells Grown on Si Substrates

With its wide bandgap and good diode performance, GaAsP is an excellent candidate for the top cell in a silicon-based multijunction tandem device. Even though the material is not lattice matched to silicon, inclusion of a graded SiGe buffer between the GaAsP layer and the Si substrate has previously been demonstrated to enable lattice matching. The SiGe layer may then serve as a high-quality current-matched bottom cell to form a tandem dual-junction structure. This paper describes the design, fabrication, analysis, and improvement of the GaAsP top solar cell in a three-terminal GaAsP/SiGe tandem solar cell on a silicon substrate. Uncertified GaAsP top cell efficiencies have been improved from 8.4% to 18.4% with bandgap voltage offsets ( $W_{{\rm oc}}$ ) of 0.48 and 0.31 V under concentration factors of 1 and 20 ×, respectively. This progress is made by improved III–V material quality, reduced series resistance, and an addition of antireflection coating. Improving the optics, material quality, and fill factor (FF) should further improve the efficiency of the GaAsP top cell in this tandem structure grown on an Si substrate.

Perovskite Solar Cells with Large-Area CVD-Graphene for Tandem Solar Cells.

Perovskite solar cells with transparent contacts may be used to compensate for thermalization losses of silicon solar cells in tandem devices. This offers a way to outreach stagnating efficiencies. However, perovskite top cells in tandem structures require contact layers with high electrical conductivity and optimal transparency. We address this challenge by implementing large-area graphene grown by chemical vapor deposition as a highly transparent electrode in perovskite solar cells, leading to identical charge collection efficiencies. Electrical performance of solar cells with a graphene-based contact reached those of solar cells with standard gold contacts. The optical transmission by far exceeds that of reference devices and amounts to 64.3% below the perovskite band gap. Finally, we demonstrate a four-terminal tandem device combining a high band gap graphene-contacted perovskite top solar cell (Eg = 1.6 eV) with an amorphous/crystalline silicon bottom solar cell (Eg = 1.12 eV).