Monolithic Tandem Solar Cells Research Articles

Interface Reactive Sputtering of Transparent Electrode for High-Performance Monolithic and Stacked Perovskite Tandem Solar Cells.

Sputtered indium tin oxide (ITO) fulfills the requirements of the top transparent electrodes (TTEs) in semitransparent perovskite solar cells (PSCs) and stacked tandem solar cells (TSCs) as well as the recombination layers in monolithic TSCs. However, the high-energy ITO particles will cause damage to the devices and reduce the photovoltaic performance. Herein, the interface reactive sputtering strategy has been proposed and implemented to construct cost-effective TTEs with high transmittance and excellent carrier transporting ability, aiming to realize high-performance semitransparent and tandem PSCs. Polyethylenimine (PEI) was chosen as the interface reactant, of which abundant amino groups on PEI can react with sputtered ITO nanoparticles so that coordination compounds can be formed during the ITO deposition process, facilitating the carrier transport at the interface of C60/PEI/ITO. Besides, the impact force of energetic ITO particles is greatly alleviated, and the intactness of the underlying C60 layer and perovskite layer is guaranteed. Thus, the prepared semitransparent subcells achieve a significantly enhanced power conversion efficiency (PCE) of 19.17%, surpassing those based on C60/ITO (11.64%). Moreover, the PEI-based devices demonstrate excellent storage stability, which maintains 98% of their original PCEs after 2000 hours. On the strength of the interface reactive sputtering ITO electrode, we successfully fabricated a stacked all-perovskite TSC with a PCE of 26.89% and a monolithic perovskite-organic TSC with a PCE of 24.33%. This work has provided a facile and instrumental solution for rendering TTEs function well in semitransparent and tandem PSCs. This article is protected by copyright. All rights reserved.

Machine Learning-Enabled Optical Architecture Design of Perovskite Solar Cells.

Perovskite solar cells, emerging as a cutting-edge solar energy technology, have demonstrated a power conversion efficiency (PCE) of >26%, which is below the theoretical limit of 33%. This study, employing a combination of neural network models and high-throughput simulation calculations, taking the single-junction FAPbI3 cell as an illustrative example, indicates that a pyramid structure, in comparison of a planar one, can increase the highest Jsc to 27.4 mA/cm2 and the PCE to 28.4%. Both Jsc and PCE surpass the currently reported experimental results. The optimized periodicity and tilt angle of the pyramid structure align with the textured structure of crystalline silicon solar cells. These results underscore the substantial development potential of neural network inverse design based on high-throughput calculations in the field of optoelectronic devices and provide theoretical guidance for the design of monolithic perovskite-silicon tandem solar cells.

Dual interface strategies enable efficient wide bandgap perovskite solar cells

High performance wide bandgap perovskite solar cells (WB-PSCs) have found widespread applications in tandem solar cells. In WB-PSCs, achieving a high conversion efficiency relies on the effective utilization of light absorption and minimization of electronic defects. In this work, electronic defects at the surface and grain boundaries of perovskite materials have been passivated by n-butylammonium bromide (BABr) to suppress carrier non-radiative recombination. Confirmed through x-ray powder diffraction and x-ray photoelectron spectroscopy spectra, ultra-thin two-dimensional (2D) perovskite layers were successfully generated on a perovskite surface. The BABr-treated devices exhibited an increased fill factor and open circuit voltage (VOC) compared to the references. Furthermore, a nanotextured electrode with a roughness of 22.98 nm was employed to trap light. The nanotextured buried interface not only promoted light utilization but also alleviated residual stress and micro-strain in the perovskite film compared to the smooth substrate. Finally, the champion WB-PSC achieved a power conversion efficiency of 20.46% in the reverse scan. These findings pave a promising path for the development of solution-processed perovskite films on nanotextured silicon substrates to improve the performance of monolithic tandem solar cells.

Bayesian Optimization with Experience for Fast Development of Monolithic Tandem Solar Cells: Simulation Case Study

AbstractMachine learning (ML) is gaining more attention in photovoltaic research and will be a vital tool in reaching record‐high power conversion efficiencies (PCE) in the near future. One area, where ML is significantly beneficial is reducing the number of experiments needed to find the optimum combination of parameters in solar cell fabrication. Bayesian optimization (BO) provides routes for quickly identifying optimum parameters in problems with large parameter space. In this work, BO algorithms utilizing previous knowledge are demonstrated to result in faster optimization of tandem solar cells, a technology rapidly gaining more interest due to its potential to deliver record‐high performance. Namely, it is shown that in the space of all possible parameter combinations that take ≈88 years to evaluate, optimum PCE can be obtained in 20 min. Moreover, it is demonstrated that methods utilizing previous knowledge outperform those that do not by yielding an increase of ≈8.9%abs. in the 1st iteration and requiring 5× less time to reach a target PCE of 38.5% across 20 different trials. Results from this work help accelerate the development of tandem solar cells by removing the need for large numbers of experiments in identifying optimum parameters.

Surface repair of wide-bandgap perovskites for high-performance all-perovskite tandem solar cells

Wide-bandgap (WBG) perovskite solar cells (PSCs) play a fundamental role in perovskite-based tandem solar cells. However, the efficiency of WBG PSCs is limited by significant open-circuit voltage losses, which are primarily caused by surface defects. In this study, we present a novel method for modifying surfaces using the multifunctional S-ethylisothiourea hydrobromide (SEBr), which can passivate both Pb-I and FA-I terminated surfaces. Moreover, the SEBr upshifted the Fermi level at the perovskite interface, thereby promoting carrier collection. This proposed method was effective for both 1.67 and 1.77 eV WBG PSCs, achieving power conversion efficiencies (PCEs) of 22.47% and 19.90%, respectively, with VOC values of 1.28 and 1.33 V, along with improved film and device stability. With this advancement, we were able to fabricate monolithic all-perovskite tandem solar cells with a champion PCE of 27.10%. This research offers valuable insights for passivating the surface trap states of WBG perovskite through rational multifunctional molecular engineering.

Simulation study of Perovskite/Si Monolithic Multijunction Solar Cell

The utilization of perovskite and crystalline-silicon (c-Si) light absorbers in multijunction solar cells presents an exciting opportunity to surpass the efficiency limit of the industry's leading single-junction c-Si solar cells. In this work, we used the Solar Cell Capacitance Simulator (SCAPS-1D) to simulate a monolithic tandem junction solar cell. The solar cell consists of two types of materials: low bandgap and high bandgap. These are layers of perovskites and Si, divided by a window layer of zinc oxide (ZnO), a buffer layer of cadmium sulfide (CdS), a recombination layer of Spiro-MeOTAD/silicon, and a heavily doped back surface field layer formed from n++Si to prevent recombination at the back surface. The impact of di fferent series and shunt resistances, as well as perovskite layer thickness and bandgap, on solar cells' photovoltaic performance has been investigated.

Solution-Processed Monolithic Tandem Perovskite/n-Si Hybrid Solar Cells Using MoO3/InZnO Bilayer-Based Interconnecting and Window Layers

A metal oxide-based interconnecting and window layer consisting of a molybdenum oxide (MoO3)/Zn-doped In2O3 (IZO) bilayer was investigated in efficient solution-processed perovskite/n-Si monolithic tandem solar cells using formamidinium cesium lead triiodide, FA0.9Cs0.1PbI3, and poly(3,4-ethylenedioxythiophene)/poly(polystyrene sulfonate) (PEDOT:PSS). The MoO3/IZO bilayer with and without Au nanoparticle play a significant role in the charge extraction and recombination within the interconnecting layer and the window layer of the top cell, respectively. A power conversion efficiency of 18–19% was achieved with a short-circuit current, Jsc, of 17.8 mA/cm2; an open-circuit voltage, Voc, of 1.48 V; and an FF of 0.74 by adjusting the layer thicknesses of MoO3 (5 nm), Au nanoparticle layer (5 nm), and sputtered IZO (42 nm for ICL and 80 nm for window layer).

Top cell design and optimization of all-chalcopyrite CuGaSe<sub>2</sub>/CuInSe<sub>2</sub> two-terminal tandem solar cells: first-principles calculations and device simulations

Solar cells have attracted much attention since they can convert solar energy directly into electricity, and have been widely utilized in manufacturing industry and people's daily life. Although the power conversion efficiency (PCE) of single-junction solar cells has gradually improved in recent years, its maximum efficiency is restricted by the Shockley-Queisser (SQ) limit of single-junction solar cells. To exceed the SQ limit and further obtain high efficiency solar cells, researchers have proposed the concept of tandem solar cells. In this work, a systematic theoretical study of chalcopyrite CuGaSe<sub>2</sub>/CuInSe<sub>2</sub> tandem solar cells was carried out by combining first-principle calculations and SCAPS-1D device simulations. Firstly, the electronic structure, defect properties and corresponding macroscopic performance parameters of CuGaSe<sub>2</sub> (CGS) were obtained by first-principles calculations, which were adopted as input parameters for subsequent device simulations of CGS solar cells. Subsequently, the simulations of single-junction CGS and CuInSe<sub>2</sub> (CIS) solar cells were carried out using SCAPS-1D software, respectively. The simulation results for the single junction CIS solar cells are in good agreement with the experimental values. For single-junction CGS cells, the device simulations revealed that CGS single-junction solar cells had the highest short-circuit current (J<sub>sc</sub>) and PCE at the growth condition of Cu-rich, Ga-rich and Se-poor chemical growth condition. Further optimization found that the open-circuit voltage (V<sub>oc</sub>) and PCE of CGS solar cells can be improved by replacing the electron transport layer (ETL) with ZnSe after the devices with the highest short-circuit current (J<sub>sc</sub>). Finally, after the optimized CGS and CIS solar cells were connected in series with two-terminal (2T) monolithic tandem solar cell, the device simulation results show that under the growth temperature of 700 K and the growth environment of Cu-rich, Ga-rich, and Se-poor, with ZnSe as the ETL, the CGS thickness of 2000 nm and the CIS thickness of 1336 nm, the PCE of 2T monolithic CGS/CIS tandem solar cell can reach 28.91 %, which is higher than the recorded efficiency of the current single-junction solar cells, and shows a good application prospect.

All-inorganic halide perovskites for air-processed “n–i–p” monolithic perovskite/organic hybrid tandem solar cells exceeding 23% efficiency

We are excited to report dynamic hot-air assisted ambient conditions processed metal ion-doped γ-CsPb(I1−xBrx)3 (Eg = 1.87 eV) wide bandgap in combination with a ternary bulk-heterojunction (Eg = 1.36 eV) narrow bandgap based monolithic hybrid tandem solar cells crossing 23% efficiency.

Matching the Photocurrent of 2‐Terminal Mechanically‐Stacked Perovskite/Organic Tandem Solar Modules by Varying the Cell Width

Photocurrent matching in conventional monolithic tandem solar cells is achieved by choosing semiconductors with complementary absorption spectra and by carefully adjusting the optical properties of the complete top and bottom stacks. However, for thin film photovoltaic technologies at the module level, another design variable significantly alleviates the task of photocurrent matching, namely the cell width, whose modification can be readily realized by the adjustment of the module layout. Herein, this concept is demonstrated at the experimental level for the first time for a 2T‐mechanically stacked perovskite (FAPbBr3)/organic (PM6:Y6:PCBM) tandem mini‐module, an unprecedented approach for these emergent photovoltaic technologies fabricated in an independent manner. An excellent I sc matching is achieved by tuning the cell widths of the perovskite and organic modules to 7.22 mm (PCE PVKT‐mod = 6.69%) and 3.19 mm (PCE OPV‐mod = 12.46%), respectively, leading to a champion efficiency of 14.94% for the tandem module interconnected in series with an aperture area of 20.25 cm2. Rather than demonstrating high efficiencies at the level of small lab cells, this successful experimental proof‐of‐concept at the module level proves to be particularly useful to couple devices with non‐complementary semiconductors, either in series or in parallel electrical connection, hence overcoming the limitations imposed by the monolithic structure.

Versatile implied open‐circuit voltage imaging method and its application in monolithic tandem solar cells

AbstractAs the efficiency of perovskite silicon tandem solar cells is increasing, the upscaling for industrial production is coming into focus. Spatially resolved, quantitative, fast, and reliable contactless measurement techniques are demanded for quality assurance and to pinpoint the cause of performance losses in perovskite silicon tandem solar cells. In this publication, we present a measurement method based on spectrally integrated photoluminescence (PL) imaging to extract subcell‐selective implied open‐circuit ( ) images from monolithic perovskite silicon tandem solar cells. We validate the approach using spectrally resolved absolute PL measurements based on an integrating sphere for the perovskite top cell and PL‐calibrated carrier lifetime images for the silicon bottom cell. Additionally, measurements of solar cells with low contact losses are used to validate the new measurement technique. We find a good agreement of the images with the validating measurements with a maximum deviation of well below 1% compared to the validation measurements.

Bimolecularly passivated interface enables efficient and stable inverted perovskite solar cells

Compared with the n-i-p structure, inverted (p-i-n) perovskite solar cells (PSCs) promise increased operating stability, but these photovoltaic cells often exhibit lower power conversion efficiencies (PCEs) because of nonradiative recombination losses, particularly at the perovskite/C 60 interface. We passivated surface defects and enabled reflection of minority carriers from the interface into the bulk using two types of functional molecules. We used sulfur-modified methylthio molecules to passivate surface defects and suppress recombination through strong coordination and hydrogen bonding, along with diammonium molecules to repel minority carriers and reduce contact-induced interface recombination achieved through field-effect passivation. This approach led to a fivefold longer carrier lifetime and one-third the photoluminescence quantum yield loss and enabled a certified quasi-steady-state PCE of 25.1% for inverted PSCs with stable operation at 65°C for >2000 hours in ambient air. We also fabricated monolithic all-perovskite tandem solar cells with 28.1% PCE.

Transparent Recombination Electrode with Dual-Functional Transport and Protective Layer for Efficient and Stable Monolithic Perovskite/Organic Tandem Solar Cells.

Rational selection and design of recombination electrodes (RCEs) are crucial to enhancing the power conversion efficiency (PCE) and stability of monolithic tandem solar cells (TSCs). Sputtered indium tin oxide (ITO) with high conductivity and excellent transmittance is introduced as RCE in perovskite/organic TSCs. To prevent high-energy ITO particles destroy the underlying material during sputtering, dual-functional transport and protective layer (C1) is employed. The styryl group in C1 can be thermally crosslinked to serve as a sputtering protective layer. Meanwhile, the conjugated phenanthroline skeleton in C1 shows high electron mobility and hole blocking capability to promote the electron transport process at the interfaces and effectively reduce charge accumulation. Monolithic perovskite/organic TSC with high PCE of 24.07% and excellent stability is demonstrated by stacking a 1.77eV bandgap perovskite layer and a 1.35eV bandgap organic active layer. This strategy provides new insights for overcoming the fundamental efficiency limits of single-junction devices and promotes the further development of TSC devices.

Surface-functionalized hole-selective monolayer for high efficiency single-junction wide-bandgap and monolithic tandem perovskite solar cells

Carbazole moiety-based 2PACz ([2-(9H-carbazol-9-yl)ethyl]phosphonic acid) self-assembled monolayers (SAMs) are excellent hole-selective contact (HSC) materials with abilities to excel the charge-transfer-dynamics of perovskite solar cells (PSCs). Herein, we report a facile but powerful method to functionalize the surface of 2PACz-SAM, by which reproducible, highly stable, high-efficiency wide-bandgap PSCs can be obtained. The 2PACz surface treatment with various donor number solvents improves assembly of 2PACz-SAM and leave residual surface-bound solvent molecules on 2PACz-SAM, which increases perovskite grain size, retards halide segregation, and accelerates hole extraction. The surface functionalization achieves a high power conversion efficiency (PCE) of 17.62% for a single-junction wide-bandgap (∼1.77 eV) PSC. We also demonstrate a monolithic all-perovskite tandem solar cell using surface-engineered HSC, showing high PCE of 24.66% with large open-circuit voltage of 2.008 V and high fill-factor of 81.45%. Our results suggest this simple approach can further improve the tandem device, when coupled with a high-performance narrow-bandgap sub-cell.

A monolithic all-perovskite tandem solar cell with 2-T, 3-T and 4-T architecture integrated

Multi-junction all-perovskite tandem solar cells (A-PTSCs) can achieve higher power conversion efficiency (PCE) value beyond the Shockley-Queisser limit of single-junction perovskite solar cells (PSCs). However, only one side of the substrate is used in traditional two-junction tandem devices architecture, so that two-terminal (2-T) tandem devices require the preparation of a high quality and complex interconnection layer (ICL) to connect the two sub-cells and four-terminal (4-T) tandem devices require two substrates for two sub-cells. Here we demonstrate a two-junction A-PTSC using a double-sided ITO (D-ITO) glass substrate. The wide bandgap (W-Eg) perovskite (1.75 eV) as the upper cell and the narrow bandgap (N-Eg) perovskite (1.21 eV) as the bottom cell are deposited on both side of the D-ITO substrate, respectively. By changing the wiring method, on a substrate, 2-T, three-terminal (3-T), and 4-T integrated A-PTSC are obtained with efficiencies of 21.17% for 2-T tandem architecture, 17.71% for 3-T and 21.55% for 4-T. The concept and design here represent a new architecture toward A-PTSCs.

Interface engineering for high-performance, triple-halide perovskite-silicon tandem solar cells.

Improved stability and efficiency of two-terminal monolithic perovskite-silicon tandem solar cells will require reductions in recombination losses. By combining a triple-halide perovskite (1.68 electron volt bandgap) with a piperazinium iodide interfacial modification, we improved the band alignment, reduced nonradiative recombination losses, and enhanced charge extraction at the electron-selective contact. Solar cells showed open-circuit voltages of up to 1.28 volts in p-i-n single junctions and 2.00 volts in perovskite-silicon tandem solar cells. The tandem cells achieve certified power conversion efficiencies of up to 32.5%.

Solvent engineering of scalable deposited wide-bandgap perovskites for efficient monolithic perovskite-organic tandem solar cells

High-quality wide-bandgap perovskite films are a key component in constructing efficient tandem solar cells. Although the efficiency of perovskite tandem devices advances rapidly in recent years, the majority of wide-bandgap perovskite films are deposited by laboratory spin-coating, which greatly hinders their commercial viability. Here, we first show that the widely-used binary solvents (DMF:DMSO) in spin-coating are incapable of producing qualified wide-bandgap perovskite films by scalable methods. It is identified that dense and uniform wide-bandgap thin films can be deposited from single-solvent NMP by blade-coating, which is mainly related to the well-controlled crystallization kinetics enabled by the formation of stable intermediate adduct. Along with a rational passivation by constructing a 2D/3D layered heterojunction, inverted perovskite devices with a bandgap of 1.8 eV deliver a champion efficiency of 18.92 %. On this basis, monolithic perovskite-organic tandem solar cells with an efficient and robust interconnection layer of “SnO2/Au/PEDOT:PSS” are fabricated, yielding a high efficiency of 22.25 % along with an impressive open-circuit voltage of 2.1 V. These results demonstrate an important step toward scalable fabrication of monolithic perovskite-organic tandem solar devices.

Minimizing electro-optical losses of ITO layers for monolithic perovskite silicon tandem solar cells

Minimizing electro-optical losses of ITO layers for monolithic perovskite silicon tandem solar cells

Integration of rough RTP absorbers into CIGS-perovskite monolithic tandems by NiOx(:Cu)+SAM Hole-transporting Bi-layers

We investigate the performance of monolithic copper-indium-gallium-selenide (CIGS)/perovskite tandem solar cells with two different CIGS bottom device absorbers: Cu(In,Ga)Se2 or Cu(In,Ga)(S,Se)2 and with three different hole-transporting layers (HTLs): NiOx + SAM, NiOx:Cu + SAM and SAM alone. NiOx(:Cu) is (2 wt% copper-doped) nickel oxide and SAM is the MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid) self-assembled monolayer. The CIGSe is fabricated by physical-vapor deposition (PVD), has a Eg ∼ 1.06eV, and a σRMS,PVD ∼ 65 nm, while the CIGSSe is fabricated by rapid-thermal processing (RTP), has a Eg ∼ 1.01eV, and a σRMS,RTP ∼ 120 nm. While the current certified, 24.2%-efficient, world-record monolithic CIGSe-perovskite tandem solar cell has previously been achieved with SAM as a stand-alone HTL, this work investigates whether SAM can yield similarly high efficiencies also on industrially compatible, very rough RTP CIGSSe absorbers. We find that the devices with SAM as stand-alone HTL suffer from severe FF and Voc losses and that NiOx:Cu is needed to act as a shunt-quenching layer below that SAM, ensuring conformal coverage of the rough bottom sub-cell surface. Within this work the highest-achieved (in-house measured) PCEs for the RTP and PVD CIGS-based tandems are 21.6% and 23.2% respectively, on a cell area of 1.08 cm2, both of which are obtained with NiOx:Cu + SAM as an HTL.

Optical simulations and optimization of perovskite/CI(G)S tandem solar cells using the transfer matrix method

In this work we employ the transfer matrix method for the analysis of optical materials properties to simulate and optimize monolithic tandem solar cell devices based on CuIn1−x Ga x Se2, CI(G)S, and perovskite (PVK) absorbers. By finding models that fit well the experimental data of the CI(G)S solar cell, the semitransparent perovskite solar cell (PSC) and the PVK/CI(G)S monolithic tandem solar cell, we were able to perform a detailed optical loss analysis that allowed us to determine sources of parasitic absorption. We found better substitute materials for the transport layers to increase the power conversion efficiency and, in case of semitransparent PSCs, sub-bandgap transmittance. Our results set guidelines for the monolithic PVK/CI(G)S tandem solar cells development, predicting an achievable efficiency of 30%.