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The exceptional optoelectronic performance and cost‐effectiveness of manufacturing have propelled organic–inorganic hybrid perovskite solar cells (PSCs) into the spotlight within the photovoltaic community. Currently, the single‐junction PSCs have achieved a certified power conversion efficiency surpassing 26%, edging closer to the illustrious Shockley–Queisser theoretical limit. To further enhance device performance, researchers are currently directing their attention toward the integration of wide‐bandgap (WBG) perovskites (Eg > 1.60 eV) as top subcells in conjunction with narrow‐bandgap materials, such as perovskite, crystalline silicon, and copper indium gallium selenium, to construct multijunction tandem devices that maximize solar spectral utilization and minimize thermal losses. However, WBG perovskites encounter challenges associated with suboptimal crystal quality, high defect density, and severe phase separation, leading to significant voltage losses and inferior performance. In this regard, extensive research has been conducted, yielding significant findings. This review article summarizes the advancements in composition engineering, additive engineering, and interface engineering of WBG PSCs. Furthermore, the applications of WBG PSCs in various tandem solar cells and their development are discussed. Finally, future prospects for the development of WBG PSCs are outlined. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) can produce solar energy that is both affordable and highly effective. Still, they currently face challenges in achieving peak performance in important areas, including sustainability, stability, and efficiency. Recent studies examine tandem perovskite solar cells based on CsPbI3 in great detail, analyzing their photovoltaic characteristics with SCAPS 1D software. This work examines the effects of multiple parameters on performance metrics, including power conversion efficiency (PCE), fill factor (FF), open-circuit voltage (Voc), and shortcircuit current (Jsc), with a focus on a multi-layered design. The photoactive layer thickness, defect densities, electrode contact quality, and operation temperatures are the factors. Compared to conventional lead-based perovskites, CsPbI3 offers advantages in terms of long-term stability, reduced moisture susceptibility, and reduced lead toxicity. However, there is an issue with achieving efficiency levels comparable to MAPbI3 and FAPbI3. The research reveals correlations between material properties and device performance by applying advanced diagnostic techniques like quantum efficiency (QE), carrier concentration, and recombination rate analysis. This information has the potential to result in material enhancements and device optimization. With a particular focus on CsPbI3, the work offers crucial insights into tandem perovskite solar cells that will advance the creation of more reliable, effective, and sustainable solar energy systems. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are gaining popularity due to their high efficiency and low-cost fabrication. In recent decades, noticeable research efforts have been devoted to improving the stability of these cells under ambient conditions. Moreover, researchers are exploring new materials and fabrication techniques to enhance the performance of PSCs under various environmental conditions. The mechanical stability of flexible PSCs is another area of research that has gained significant attention. The latest research also focuses on developing tin-based PSCs that can overcome the challenges associated with lead-based perovskites. This review article provides a comprehensive overview of the latest advances in materials, fabrication techniques, and stability enhancement strategies for PSCs. It discusses the recent progress in perovskite crystal structure engineering, device construction, and fabrication procedures that has led to significant improvements in the photo conversion efficiency of these solar devices. The article also highlights the challenges associated with PSCs such as their poor stability under ambient conditions and discusses various strategies employed to enhance their stability. These strategies include the use of novel materials for charge transport layers and encapsulation techniques to protect PSCs from moisture and oxygen. Finally, this article provides a critical assessment of the current state of the art in PSC research and discusses future prospects for this technology. This review concludes that PSCs have great potential as a low-cost alternative to conventional silicon-based solar cells but require further research to improve their stability under ambient conditions in view of their definitive commercialization. [ABSTRACT FROM AUTHOR]

Printing a large‐area bismuth vanadate photoanode offers a promising approach for cost‐effective photoelectrochemical (PEC) water splitting. However, the light absorption trade‐off with charge transfer, as well as stability issues always lead to poor PEC efficiency. Here, the solution‐processed recipe is advanced with BiI3 dopant for the printed deposition with controllable crystal growth. The resultant BiVO4 films prefer (001) orientation with nanorod feature on substrate, allowing a faster charge transfer and improved photocurrent. The BiVO4 photoanode in tandem with perovskite solar module delivers an operating photocurrent density of 5.88 mA cm−2 at zero bias in 3.11 cm2 active area under AM 1.5 G illumination, yielding a solar‐to‐hydrogen efficiency as high as 7.02% for unbiased water splitting. Equally important, the stability of the aged BiVO4 rods has been addressed to distinguish phase segregation at surface. The photocatalysis degradation composes of vanadium loss and Bi2O3 enriching at the surface, opening a lid on the long‐term stability of BiVO4 photoanodes. [ABSTRACT FROM AUTHOR]

Designing photoanode semiconducting materials with visible‐light absorption and minimal charge‐carrier recombination for achieving efficient solar‐to‐hydrogen (STH) conversion is challenging. Here, hybrid Ta3N5 nanorods and thin films are developed on transparent GaN/Al2O3 substrates. A Ta3N5 photoanode with a loaded cocatalyst achieves the best current density, i.e. 10.8 mA cm−2, at 1.23 V versus the reversible hydrogen electrode under simulated AM 1.5G solar illumination. In a tandem configuration with dual‐CuInSe2 photovoltaic cells, this semi‐transparent photoanode achieves a reproducible STH energy conversion efficiency of ≈12% (the highest among photocatalytic materials), and remains at more than 10% for 6.7 h of tandem device operation. Detailed transient absorption spectroscopy and theoretical analysis indicates that this high performance originates from efficient light absorption and hole utilization inside the Ta3N5 material. The results show the feasibility of suppressing dominant optical and charge‐carrier‐ recombination losses by using nanostructured visible‐light‐absorbing materials for practical STH conversion. [ABSTRACT FROM AUTHOR]

This study evaluates the effect of silver alloying, stoichiometry, and deposition temperature of wide‐gap (Ag,Cu)GaSe2 (ACGS) absorber films for solar cell applications. Devices using a standard CdS buffer exhibit a strong anticorrelation between the open‐circuit voltage (VOC) and short‐circuit current density (JSC), with VOC decreasing and JSC increasing toward stoichiometric absorber composition. Increasing the ACGS deposition temperature leads to larger grains and improved JSC, while VOC is not affected. By adding more silver to the absorber (maximum tested [Ag]/([Ag]+[Cu]) [AAC] = 0.4), the widening of the space charge region (SCR) significantly enhances carrier collection. Experimental quantum efficiency spectra can be accurately simulated when assuming a very low diffusion length and perfect collection in the SCR. The highest efficiency of 8.3% (without antireflection coating [ARC]) is reached for an absorber with AAC = 0.4 grown at 600 °C. Replacing CdS by a (Zn,Sn)O buffer with lower electron affinity strongly mitigates interface recombination. Moreover, the VOC–JSC anticorrelation is not evident anymore and the highest efficiency of 11.2% (11.6% w/ARC, VOC = 985 mV, JSC = 18.6 mA cm−2, fill factor = 61.0%) is reached for a close‐stoichiometric ACGS solar cell with AAC = 0.4 processed at 650 °C. [ABSTRACT FROM AUTHOR]

Compared with the single‐junction perovskite solar cells, the perovskite/perovskite tandem solar cells have the advantages of lower cost and higher power conversion efficiency (PCE). Herein, both two‐terminal (2‐T) and four‐terminal (4‐T) perovskite/perovskite tandem solar cells with all‐inorganic perovskite as the top cell absorption layer and narrow bandgap perovskite MASn0.5Pb0.5I3 material as the bottom cell absorption layer are studied. To effectively improve the photon absorption ratio and performance of the 4‐T tandem device, both reflection and parasitic absorption should be reduced. Afterward, by optimizing the doping concentration of the carrier transport layer, a 4‐T all‐perovskite tandem solar cell with a high PCE of 30.45% is obtained. For the 2‐T all‐perovskite tandem device, the all‐inorganic perovskites with different halogen components (CsPbI3−xBrx, 0 ≤ x ≤ 3) are used as the absorption layer of the top cell, respectively. Through the optimization of the current matching of the subcell, the photoelectric field distribution, the parasitic absorption of the device, etc., an optimal PCE of 27.86% is obtained based on 2‐T CsPbI2Br/MASn0.5Pb0.5I3 tandem device. This study provides a guide for achieving high performance perovskite/perovskite tandem solar cells. [ABSTRACT FROM AUTHOR]

With the development of modern technology, the functions of smart windows are expected to be more abundant apart from reducing energy consumption. A viable and popular solution is to develop a versatile product. Here a multi‐functional tandem device enabled by ionic gels to form a smart glass that can be applied in manifold scenarios, is reported. The ionic gels successfully fulfill the multiple tasks of simultaneously being electrolytes, ion storage medium, as well as transparent electrodes, and help heighten the overall transparency of the devices. The novel tandem configuration simply consists of five stacking functional layers and is universal for DC‐driven electrochromic and AC‐driven electroluminescent sub‐devices. The newly‐developed devices demonstrate magnificent characteristics of high and tunable transparency (0–77%), selective infrared shielding ability, diversified displaying and decoration, excellent stability (3000 cycles), and even flexibility. Multifarious application scenarios of the structure in diversified device forms are proposed and presented. The proposed device architecture provides a facile methodology to fabricate functional devices and will provoke infinite novel ideas for developing the next‐generation smart windows. [ABSTRACT FROM AUTHOR]

Narrowband photodetectors (PDs) are sought after for many applications requiring selective spectral response. The most common systems combine optical bandpass filters with broadband photodiodes. This work reports a method to obtain a narrowband response in a perovskite PD by the monolithic integration of a perovskite photoconductor and a perovskite photodiode. The spectral response of the tandem PD is determined by the bandgap energy difference of the two perovskites, and exhibits a full width at half maximum below 85 nm, an external quantum efficiency up to 68% and a high specific detectivity of ≈1012 Jones in reverse bias, enabling the device to detect weak light signals. The absorption profile of the narrowband PD can be tuned by changing the thickness and bandgap of the wide bandgap perovskite absorber. [ABSTRACT FROM AUTHOR]

Herein, the performance of wide‐gap Cu(In,Ga)Se2 (CIGS) and (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells with In2O3:Sn (ITO) and In2O3:H (IOH) as transparent back contact (TBC) materials is evaluated. Since both TBCs restrict sodium in‐diffusion from the glass substrate, fine‐tuning of a NaF precursor layer is crucial. It is found that the optimum Na supply is lower for ACIGS than for CIGS samples. An excessive sodium amount deteriorates the solar cell performance, presumably by facilitating GaOx growth at the TBC/absorber interface. The efficiency (η) further depends on the absorber stoichiometry, with highest fill factors (and η) reached for close‐stoichiometric compositions. An ACIGS solar cell with η = 12% at a bandgap of 1.44 eV is processed, using IOH as a TBC. The best CIGS device reaches η = 11.2% on ITO. Due to its very high infrared transparency, IOH is judged superior to ITO for implementation in a top cell of a tandem device. However, while ITO layers maintain their conductivity, IOH films show an increased sheet resistance after absorber deposition. Chemical investigations indicate that incorporation of Se during the initial stage of absorber processing may be responsible for the deteriorated conductivity of the IOH back contact in the final device. [ABSTRACT FROM AUTHOR]

Silicon‐based tandem solar cells are regarded as one of the most feasible ways to break the single‐junction Shockley–Queisser limit efficiency and further reduce the cost of solar electricity. Recently, wide‐bandgap (≈1.7 eV) perovskite solar cells have drawn intense research interest as the top cell for Si‐based tandem devices. Despite significant progress in device efficiency, the unsatisfactory stability of perovskites is still a huge concern. Besides halide perovskites, there are many inorganic semiconductors worthy of investigation. It is believed that cadmium selenide, a binary compound enjoying outstanding optoelectronic properties, high stability, and low cost, is very promising as the top cell for Si‐based tandem devices. Herein, the CdSe thin‐film solar cells that have been neglected for 3 decades are revisited. Using rapid thermal evaporation, high‐quality CdSe thin films with large grain size, high‐photoluminescence, small Stokes shift, and intrinsic n‐type conductivity are obtained. Furthermore, CdSe solar cells are redesigned and a champion efficiency of 6.00% is achieved. Through in‐depth analysis, it is identified that bulk and interface defects limit the open‐circuit voltage and hence device performance. This work highlights the great potential of CdSe solar cells as top cells for Si‐based tandem devices. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) exhibit size-tunable optical properties, making them suitable for efficient light-sensing and light-emitting devices. Tandem devices that can convert near-infrared (NIR) to visible (Vis) signals can be fabricated by integrating an NIR-sensing QD device with a Vis electroluminescence (EL) QD device. However, these devices require delicate control of the QD layer during processing to prevent damage to the predeposited QD layers in tandem devices during the subsequent deposition of other functional layers. This has restricted attainable device structures for QD-based upconversion devices. Herein, we present a modular approach for fabricating QD-based optoelectric upconversion devices. This approach involves using NIR QD-absorbing (Abs) and Vis QD-EL units as building modules, both of which feature cross-linked functional layers that exhibit structural tolerance to dissolution during subsequent solution-based processes. Tandem devices are fabricated in both normal (EL unit on Abs unit) and inverted (Abs unit on EL unit) structures using the same set of NIR QD-Abs and Vis QD-EL units stacked in opposite sequences. The tandem device in the normal structure exhibits a high NIR photon-to-Vis-photon conversion efficiency of up to 1.9% in a practical transmissive mode. By extending our modular approach, we also demonstrate a three-stack tandem device that incorporates a single NIR-absorbing unit coupled with two EL units, achieving an even higher conversion efficiency of up to 3.2%.

Solar cells are promising devices for converting sunlight into electrical energy. Tandem solar devices, which combine multiple sub cells with complementary absorption spectra, offer a potential strategy to enhance the overall power conversion efficiency (PCE). In this work, the design and performance of organic/CIGS tandem solar devices are investigated. The initial tandem cell comprises two sub cells, namely an organic-based PM6:m-DTC-2 F top cell and CIGS bottom cell. The organic and CIGS cells show a PCE of 12.20% and 20.10%, respectively, where the initial results are based on calibrated cells reproduced from experimental studies. Accordingly, the initial tandem PM6:m-DTC-2 F/CIGS cell shows a PCE of 22.75%. The study focuses on optimizing the PCE via different approaches. Firstly, through the exploration of different hole transport layers (HTLs) of the front cell. Secondly, by investigating the matched current condition between the front and rear cells. Moreover, the doping effect of the CIGS film is investigated. Finally, optimization of the defect concentrations in the absorbers is introduced. These optimizations result in open circuit voltage (V oc) of 1.89 V with short circuit current (J sc) of 17.55 mA/cm2, and a fill factor (FF) of 82.79%. Consequently, the PCE of the optimized tandem cell is further enhanced to 27.46%. Further, the stability of the proposed tandem cell is evaluated under varying temperatures, and its composition of flexible materials makes it a promising candidate for wearable applications. [ABSTRACT FROM AUTHOR]

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials, based on polycyclic aromatic frameworks, have shown promise in achieving narrow-band emission and high luminous efficiency. In this study, we investigate the performance of a blue MR-TADF material, 2′2'2''-(1,3,5-triazine-2,4,6-triyl) tris(9-(2-(naphthalen-2-yl)phenyl)-9H-carbazole) (TBN-TPA), in tandem OLED devices. Single emitter unit and two emitter unit tandem OLED devices with blue MR-TADF material were explored with optical modeling simulation. More importantly, the tandem architecture assists in realizing narrow-band emission and high color purity via optical interference and microcavity effects, which are essential for meeting BT 2020 standards. TBN-TPA achieves narrow full width at half maximum down to 24 nm and CIE coordinates approaching the blue region in tandem devices. Our work highlights the significant advantages of combining tandem architectures and emerging MR-TADF emitters for developing high-performance OLEDs with both high efficiency and wide color gamut. This is the first demonstration of using tandem OLED architecture to improve both efficiency and color purity of a blue multi-resonance TADF emitter. Further research on optimizing tandem structures and designing advanced MR-TADF materials will promote the applications of OLED displays. • Single-emissive and dual-emissive layer blue MR-TADF tandem OLED devices were explored with optical modeling simulation. • The tandem architecture assists in realizing narrow-band emission and high color purity via optical interference and microcavity effects with a narrow FWHM of 24 nm and CIE coordinates approaching the blue region in tandem devices. [ABSTRACT FROM AUTHOR]

While multi-junction geometries have the potential to boost the efficiency of organic solar cells, the experimental gains yet obtained are still very modest. This work proposes an alternative spectral splitting device concept in which various individual semiconducting junctions with cascading bandgaps are laid side by side, thus the name RAINBOW. Each lateral sub-cell receives a fraction of the spectrum that closely matches the main absorption band of the given semiconductor. Here, simulations are used to identify the important material and device properties of each RAINBOW sub-cell. Using the resulting design rules, three systems are selected, with narrow, medium, and wide effective bandgaps, and their potential as sub-cells in this geometry is experimentally investigated. With the aid of a custom-built setup that generates spectrally spread sunlight on demand, the simulations are experimentally validated, showing that this geometry can lead to a reduction in thermalization losses and an improvement in light harvesting, which results in a relative improvement in efficiency of 46.6% with respect to the best sub-cell. Finally, a working proof-of-concept monolithic device consisting of two sub-cells deposited from solution on the same substrate is fabricated, thus demonstrating the feasibility and the potential of the RAINBOW solar cell concept., (© 2023 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)