Silicon Tandem Solar Cells Research Articles

Optical optimization of double-side-textured monolithic perovskite-silicon tandem solar cells for improved light management.

Tandem configuration-containing perovskite and silicon solar cells are promising candidates for realizing a high power conversion efficiency of 30% at reasonable costs. Silicon solar cells with planar front surfaces used in tandem devices cause high optical losses, which significantly affects their efficiency. Moreover, some studies have explored the fabrication of perovskites on textured silicon cells. However, due to improper texturing, light trapping is not ideal in these devices, which reduces the efficiency. In this work, we optimized the pyramid height of textured silicon cells and efficiently characterized them to achieve enhanced light trapping. Two different kinds of perovskites, namely, Cs0.17FA0.6Pb(Br0.17I0.7)3 and Cs0.25FA0.6Pb(Br0.20I0.7)3 with wide bandgaps were conformally deposited on textured silicon cells, and the performance of these flat and fully textured tandem devices was numerically analyzed. The thickness of each layer in the tandem cell was optimized in a way to ensure a perfect current match between the top perovskite and bottom silicon subcells. The results indicated that the textured tandem configuration enhances light absorption over a broad spectral range due to the optimized pyramid height compared to flat surfaces. Eventually, the photovoltaic parameters of the proposed tandem cell were compared with the already existing structures, and our design supports large values of open circuit voltage (Voc) = 1.78 V, short circuit current density (Jsc) = 20.09 mA cm−2, fill factor (FF) = 79.01%, and efficiency (η) = 28.20% compared to other kinds of tandem solar cells.

Hybrid Evaporation/Spray-Coating Process for a Simplified and Controllable Production of Perovskite Solar Cells

Recently, hybrid processing using evaporation and spin-coating has been applied for the fabrication of perovskite silicon tandem solar cells with record power conversion efficiencies (PCEs) of 25.2%. To achieve large area, high-throughput production of solar cells, spray-coating, a well-known scalable method used in the industry, has advantages over spin-coating. Therefore, we apply a hybrid method using the evaporation of PbI2 and spraying of methylammonium iodide (MAI) for the fabrication of perovskite solar cells. This article presents a systematic study of sprayed MAI amount and processing parameters on the performance of solar cells. We find clear correlations between the processing parameters of the sprayed MAI, the crystallinity of CH3NH3PbI3 and the PCE of the resulting PSCs. High crystallinity and morphology of the CH3NH3PbI3 film is achieved using a slow nozzle speed of 30 mm·s−1. An average PCE of 11.6% ± 3.1% (maximum PCE of 14.3%, stabilized PCE of 10%) was achieved with a normalized MAI amount of 3.4, which represent the flow rate of 0.17 ml·min−1, nozzle speed of 30 mm·s−1, MAI concentration of 9 mg·mL−1, and one single spray pass. Moreover, we successfully show a proof-of-concept of this method for the deposition of homogenous perovskite layers on pyramidal textured silicon.

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.

Stable Cesium Formamidinium Lead Halide Perovskites: A Comparison of Photophysics and Phase Purity in Thin Films and Single Crystals

The stability of the active layer is an underinvestigated aspect of metal halide perovskite solar cells. Furthermore, the few articles on the subject are typically focused on thin films, which are complicated by the presence of defects and grain boundaries. Herein, a different approach is taken: a perovskite composition that is known to be stable in single crystal form is used, and its (photo‐)physical properties are studied in the form of spin‐coated thin films. The perovskites are lead‐based with cesium and formamidinium as the A‐site cations and iodide and bromide as the halide anions, with the formula Cs0.1FA0.9PbI3−xBrx. These compounds show high potential in terms of stability in single crystal form and closely resemble the compounds that have successfully been used in highly efficient perovskite–silicon tandem solar cells. It is found that a small difference in bromine content (x = 0.45 vs 0.6) has a significant impact in terms of the phase purity and charge carrier lifetimes, and conclude that the thin films of Cs0.1FA0.9PbI2.55Br0.45 have good potential for the use in optoelectronic devices.

Two‐terminal Perovskite silicon tandem solar cells with a high‐Bandgap Perovskite absorber enabling voltages over 1.8 V

AbstractPerovskite silicon tandem solar cells are a promising technology to overcome the efficiency limit of silicon solar cells. Although highest tandem efficiencies have been reported for the inverted p‐i‐n structure, high‐efficiency single junction perovskite solar cells are mostly fabricated in the regular n‐i‐p architecture. In this work, regular n‐i‐p perovskite solar cells with a high‐bandgap mixed cation mixed halide absorber suitable for tandem solar cells are investigated by compositional engineering and the open‐circuit voltage is improved to over 1.12 V using a passivating electron contact. The optimized perovskite solar cell is used as a top cell in a monolithic perovskite silicon tandem device with a silicon heterojunction bottom cell allowing for voltages up to 0.725 V. The tandem solar cells with an active area of 0.25 cm2 achieve record open‐circuit voltages of up to 1.85 V and have efficiencies over 20%. Analyzing the perovskite absorber by spatially resolved photoluminescence measurements shows a homogenous and stable emission at ~ 1.7 eV which is an optimal value for tandem applications with silicon. The tandem solar cells are mainly limited due to a low current. A spectrometric characterization reveals that the perovskite solar cell is current limiting which could be improved by a thicker perovskite absorber.

Energy yield analysis of textured perovskite silicon tandem solar cells and modules.

Perovskite silicon tandem solar cells combine potentially low production costs with the ability to surpass the efficiency limit of silicon single junction solar cells. Optical modeling and optimization are crucial to achieve this ambitious goal in the near future. The optimization should seek to maximize the energy yield based on realistic environmental conditions. This work analyzes the energy yield of perovskite silicon tandem solar cells and modules based on realistic experimental data, with a special focus on the investigation of surface textures at the front and rear side of the solar cell and its implication for reflection as well as parasitic absorption properties. The investigation reveals a 7.3%rel higher energy yield for an encapsulated tandem cell with a textured front side compared with an encapsulated high efficiency single junction solar cell with 24.3% harvesting efficiency for irradiance data of the year 2014 in Freiburg/Germany.

Performance Study of the Micromorph Silicon Tandem Solar Cell Using Silvaco TCAD Simulator

This paper is concerned with the numerical modelling of a micromorph silicon tandem solar cell (a-Si:H/µc-Si:H), under series (two-terminal: 2T) and independent (four-terminal: 4T) electrical connection. The study is performed using the simulation software Silvaco TCAD. Both the initial (un-degraded or annealed) state, and the light induced degradation one (well-known Staebler–Wronski effect in a-Si:H) are considered for the studied solar cell, operating under the standard global solar spectrum (AM1.5G). The 2T- and 4T-device optimization is carried out under the effects of the intrinsic (i)-layer thickness of the two sub-cells, and the free carrier mobilities through these layers. By increasing the i-layer thickness of the two sub-cells, the 2T-micromorph tandem cell reveals an optimal conversion efficiency $$\eta$$ of 10% and 7.77% corresponding, respectively, to the initial and degraded states. The 4T-configuration exhibits a relatively better $$\eta$$ of 10.94% at initial state, reduced only to 9.59% at the degraded one. Further improvement of the 2T and 4T-cell output parameters is obtained by increasing the free carrier mobilities, particularly through the top-cell i-layer. By this way, the better $$\eta$$ is also ensured by the 4T-device, which displays an initial state- $$\eta$$ of 12.31%, reduced only to 11.43% at the degraded state. However, the improved efficiencies reached by the 2T-configuration are 11.87% and 10.41% corresponding, respectively, to the initial and degraded states.

The Role of Surface Passivation Layer Preparation on Crystallization and Optoelectronic Performance of Hybrid Evaporated-Spincoated Perovskite Solar Cells

The main advantages of the organic–inorganic halide perovskite solar cell technology are high efficiencies achieved after short development time in combination with rather simple solution-based processing. In this paper, we address remaining challenges by presenting a low-temperature two-step hybrid evaporation-spincoating method that combines high reproducibility with easy fabrication and high stabilized efficiencies, which is compatible with the processing of pervoskite silicon tandem solar cells and avoids using hazardous solvents such as dimethylformamide and dimethylsulfoxide. Lead iodide (PbI2) is thermally evaporated and subsequently converted into a compact crystalline perovskite layer by methylammonium iodide spincoating. Moreover, the role of the interface passivation between perovskite absorber and electron transport layer on crystallization and optoelectronic properties of the perovskite absorber is investigated within a systematic thickness and concentration variation of [6, 6]-phenyl-C61-butyric acid methyl ester passivation layer and by analyzing charge extraction with spatial and time resolved photoluminescence measurements. With an optimized charge extraction, 18.2% stabilized efficiency under one sun illumination is achieved. This is the highest value reported so far for the single junction perovskite solar cells made by a two-step hybrid evaporation-spincoating method.

Modeling of the tandem III–V dilute nitride bulk or quantum engineered/silicon solar cells

Tandem silicon solar cells are designed in order to lower the levelized cost of solar electricity by increasing the cell’s efficiency to more than 30%. Dual junction thin film III–V/Si cell efficiencies are limited to 20% because of high dislocation densities (>106 cm−2) due to lattice mismatch between them. GaAsyP1−x−yNx has a lattice constant matched with silicon at y = 4.7*x − 0.1 and has an optimal bandgap i.e. between 1.7 and 1.9 eV for tandem III–V’s with Si. This work designs a p-i-n GaAsPN/GaP symmetric or asymmetric (resonant thermos tunneling) multi-quantum well (MQW) device for a top sub-cell of a dual junction silicon tandem to minimize the effect of the degraded minority carrier transport properties of bulk dilute nitride layers and presents the simulated solar cell properties using a realistic drift-diffusion approach. Using extracted experimental spectral responses as well as other solar cell parameters of various silicon solar cell like: HIT, PERC, IBC etc, the tandem efficiencies of designed p-i-n MQWs devices in conjunction with silicon solar cells have been evaluated. The tandem efficiency of an optimized p-i-n MQWs device under AM 1.5 G spectrum can exceed 33% when in conjunction with a 25.6% efficient HIT silicon solar cell.

Highly efficient monolithic perovskite silicon tandem solar cells: analyzing the influence of current mismatch on device performance

We present a highly efficient monolithic perovskite/silicon tandem solar cell and analyze the tandem performance as a function of photocurrent mismatch with important implications for future device and energy yield optimizations.

Enhancing light absorption in a thin film silicon tandem solar cell fabricated on a reactive ion etched nano-structured glass surface

The efficient capture and absorption of light are important aspects in improving the photovoltaic conversion efficiency of a solar cell. In a two-terminal tandem device, the output current density is limited by the lowest current-generating component sub-cell. We attempted by experiment to improve the current density of both sub-cells, using an inverted pyramid-type textured glass substrate. One of the two surfaces of the glass substrates was textured by semi-anisotropic reactive ion etching (RIE) with a 100 sccm flow rate of SF6 gas, and with 7 µm × 7 µm square-shaped etch masks, and obtained an optimum texture of base dimension ~7 µm, height ~8.5 µm, tip diameter ~75 nm and tip to tip separation between neighboring pyramids were about 9 µm. Tandem solar cells that were fabricated on these textured surfaces receive light from the base of these micro-pyramids, thereby enhancing light absorption in the active layers of the device. The shape of the texture and orientation of layers of the tandem solar cell ensured a longer optical path inside the solar cell, leading to higher optical absorption and an improvement in device performance. We observed an increase in the short circuit current density from 11.52 to 14.30 mA cm−2, and in the device efficiency from 11.97% to 14.22%.

High Efficiency Inorganic/Inorganic Amorphous Silicon/Heterojunction Silicon Tandem Solar Cells

We investigated high-efficiency two-terminal tandem photovoltaic (PV) devices consisting of a p/i/n thin film silicon top sub-cell (p/i/n-TFS) and a heterojunction with an intrinsic thin-layer (HIT) bottom sub-cell. We used computer simulations and experimentation. The short-circuit current density (Jsc) of the top sub-cell limits the Jsc of the p/i/n-TFS/HIT tandem PV device. In order to improve the Jsc of the top sub-cell, we used a buffer-layer at the p/i and i/n interface and a graded forward-profile (f-p) band gap hydrogenated amorphous silicon germanium active layer, namely i-layer, in the top sub-cell. These two approaches showed a remarkable raise of the top sub-cell’s Jsc, leading to the increase of the Jsc of the PV tandem device. Furthermore, in order to minimize the optical loss, we employed a double-layer anti-reflective coating (DL-ARC) with a magnesium fluoride/indium tin oxide double layer on the front surface. The reduction in broadband reflection on the front surface (with the DL-ARC) and the enhanced optical absorption in the long wavelength region (with the graded f-p band gap) resulted in the high Jsc, which helped achieve the efficiency up to 16.04% for inorganic-inorganic c-Si-based tandem PV devices.

Minimizing Current and Voltage Losses to Reach 25% Efficient Monolithic Two-Terminal Perovskite–Silicon Tandem Solar Cells

The rapid rise in efficiency and tunable bandgap of metal-halide perovskites makes them highly attractive for use in tandems on silicon. Recently we demonstrated a perovskite–silicon monolithic two...

Characterization of p-type nitrogen-doped cuprous oxide/n-type hydrogenated microcrystalline silicon tunnel recombination junction for perovskite/crystalline silicon tandem solar cells

We investigated tunnel recombination junction (TRJ) structures using p-type nitrogen-doped cuprous oxide (Cu2O:N) and n-type silicon-based thin films for perovskite/heterojunction crystalline silicon monolithic tandem solar cells. The TRJ structure using n-type hydrogenated amorphous silicon showed non-ohmic behavior. On the other hand, the TRJ structure using n-type hydrogenated microcrystalline silicon (µc-Si:H) showed ohmic behavior with sufficiently low contact resistance. This indicates that the p-type Cu2O:N/n-type µc-Si:H junction is promising for the TRJ in perovskite/heterojunction crystalline silicon monolithic tandem solar cells.

Adjustment of the Band Gap Energy According to Sizes of some Cubic Nanosemiconductors of IV, III-V and II-VI Groups

The present work focuses on the modeling of the quantum confinement for several cubic semiconductors of the IV, IV-IV, III-IV, II-VI groups. In this way, we improve the actual methods of the band gap energy adjustment as function of the nanosemiconductors sizes. First, we used the Effective Mass Approximation (EMA) to investigate several confinement regimes such as weak, medium and strong. Then to ensure a good adjustment of this band gap energy, we recalculated the holes and the electrons effective masses of the cubic semiconductors via the K-P theory, the Luttinger parameters, and various interpolations. The results are compared with two other methods: a theoretical model of the Hyperbolic Band (HBM) and experimental method of the absorption spectra and photoluminescence. We found a better adjustment of the band gap energy according to nanosemiconductors size. These results may enhance considerably the efficiency of solar cells based on quantum dots by optimizing the nano-semiconductors size for each junction and converting the maximum of the solar spectrum. Indeed, we have found that the optimal quantum dot radii of all silicon tandem solar cells are 1.1nm for the upper junction and 1.5nm for the middle junction.

Variation in efficiency with change in band gap and thickness in thin film amorphous silicon tandem heterojunction solar cells with AFORS-HET.

Numerical simulation of both single and double absorbing layers in amorphous silicon thin film solar cell is performed with the use of AFORS-HET. A single absorbing layer solar cell with both a-SiH and a-SiGeH is designed and compared with a tandem heterojunction solar cell, a-SiC/a-SiH/a-Si(i)/a-SiGeH. Design parameters are investigated, compared and optimized. The maximum efficiency for each single absorbing layer and for a tandem heterojunction thin film solar cell, a-SiC/a-SiH/a-Si(i)/a-SiGeH, is predicted. The results are validated by comparing with two different method of analysis.

Nanophotonic light management for perovskite–silicon tandem solar cells

Currently, perovskite–silicon tandem solar cells are one of the most investigated concepts for overcoming the theoretical limit for the power conversion efficiency of silicon solar cells. For monolithic tandem solar cells, the available light must be distributed equally between the two subcells, which is known as current matching. For a planar device design, a global optimization of the layer thicknesses in the perovskite top cell allows current matching to be reached and reflective losses of the solar cell to be minimized at the same time. However, even after this optimization, the reflection and parasitic absorption losses add up to 7 mA / cm2. In this contribution, we use numerical simulations to study how well hexagonal sinusoidal nanotextures in the perovskite top-cell can reduce the reflective losses of the combined tandem device. We investigate three configurations. The current density utilization can be increased from 91% for the optimized planar reference to 98% for the best nanotextured device (period 500 nm and peak-to-valley height 500 nm), where 100% refers to the Tiedje–Yablonovitch limit. In a first attempt to experimentally realize such nanophotonically structured perovskite solar cells for monolithic tandems, we investigate the morphology of perovskite layers deposited onto sinusoidally structured substrates.

Perovskite–silicon tandem solar modules with optimised light harvesting

Demonstration of efficient, large-area scalable perovskite–silicon tandem solar modules with optimised light management.

Development of Sputter Processed Perovskite Films Toward Tandem Solar Cells

Tandem solar cells which combines several solar cells in series have been investigated to achieve high efficiency solar cells. Recently, perovskite/crystalline silicon tandem solar cells have attracted much attention as promising tandem structure because these solar cells have high external quantum efficiency in different wavelength range. There is a report on simulated efficiency of two terminal perovskite/crystalline silicon tandem solar cells. In that report, projected efficiency of over 30% is suggested by using inverted pyramid structure. However, most of perovskite solar cells are fabricated by solution process which is not suitable way for textured substrates, indicating that it is difficult to achieve such structured tandem solar cells in current conventional process. To overcome this problem, we focused on sputtering process. Sputtering can achieve homogeneous films even the substrate has large roughness such as textured substrates. Therefore, it is expected that sputtering is suitable method to achieve high efficient tandem solar cells. In addition, there are no reports on sputtered perovskite films which are used for solar cells. In this work, we fabricated perovskite films by sputtering and investigated the characteristics. In this work, we tried to fabricate CH3NH3PbI3 perovskite films which is commonly used as light absorber. The perovskite films were obtained from sputtered PbI2 films. PbI2 sputtering target was fabricated from PbI2 powder using a pressing under 10 MPa on stainless plate. Then, PbI2 films were deposited on glass substrates by RF sputtering using the PbI2 target. The sputtering condition was Ar atmosphere, under 1 Pa at room temperature. Perovskite films were obtained by reacting sputtered the PbI2 films and CH3NH3I gas in petri dish. The obtained perovskite films were characterized by X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) observation. Figure 1 shows XRD pattern of a perovskite film obtained from sputtered PbI2 film. Sputter processed perovskite films showed typical diffraction patterns of CH3NH3PbI3 perovskite films and had similar peaks to solution processed perovskite films. Figure 2 shows a cross sectional SEM image of a PbI2 film sputtered on fluorine-doped tin oxide (FTO) and TiO2 coated glass substrate. This image clearly indicates that homogeneous PbI2 and/or perovskite films could be fabricated by sputtering even if the substrates have large roughness. This result suggested sputtering is promising process to achieve high efficiency tandem solar cells. Figure 1

Light management of tandem solar cells on nanostructured substrates

We report the use of nanostructured substrates as a simple approach to improve the performance of tandem micromorph silicon solar cells. In the proposed approach, nanostructured substrates are produced using a low-cost, self-assembled growth process. The use of a nanostructured substrate coated with a thick transparent conductive oxide electrode layer enables the conformal deposition of the tandem solar cell absorber layers while allowing the solar cell to exhibit a modified surface morphology caused by the underlying nanostructured morphology. Using this nanostructured substrate approach, we demonstrated a 78% relative enhancement in the conversion efficiency of a tandem micromorph silicon cell on a nanostructured substrate compared to a standard tandem micromorph cell deposited onto a flat substrate.