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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%.

The maximum photocurrent in tandem organic solar cells (TOSCs) is often obtained by increasing the thicknesses of sub‐cells, which leads to recombination enhancement of such devices and compromises their power conversion efficiency (PCE). In this work, an efficient interconnecting layer (ICL) is developed, with the structure ZnO NPs:PEI/PEI/PEDOT:PSS, which enables TOSCs with very good reproducibility. Then, it is discovered that the optimal thickness of the front sub‐cell in such TOSCs can be reduced by increasing the proportion of a non‐fullerene acceptor in the active layer. The non‐fullerene acceptor used in this work has a much larger absorption coefficient than the donor in the front sub‐cell, and the absorption reduction of donor can be well complemented by that of the acceptor when increasing the acceptor proportion, thus leading to a significant overall absorption enhancement even with a thinner film. As a result, the optimal thickness of the front sub‐cell is reduced and its charge recombination is suppressed. Ultimately, the use of this ICL combined with fine‐turning of the composition in the front sub‐cell enables an efficient TOSC with a very high fill factor of 78% and an excellent PCE of 18.71% (certified by an accredited institute to be 18.09%) to be obtained. [ABSTRACT FROM AUTHOR]

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]

Here, highly efficient and stable monolithic (2‐terminal (2T)) perovskite/PbS quantum dots (QDs) tandem solar cells are reported, where the perovskite solar cell (PSC) acts as the front cell and the PbS QDs device with a narrow bandgap acts as the back cell. Specifically, ZnO nanowires (NWs) passivated by SnO2 are employed as an electron transporting layer for PSC front cell, leading to a single cell PSC with maximum power conversion efficiency (PCE) of 22.15%, which is the most efficient NWs‐based PSCs in the literature. By surface passivation of PbS QDs by CdCl2, QD devices with an improved open‐circuit voltage and a PCE of 8.46% (bandgap of QDs: 0.92 eV) are achieved. After proper optimization, 2T and 4T tandem devices with stabilized PCEs of 17.1% and 21.1% are achieved, respectively, where the 2T tandem device shows the highest efficiency reported in the literature for this design. Interestingly, the 2T tandem cell shows excellent operational stability over 500 h under continuous illumination with only 6% PCE loss. More importantly, this device without any packaging depicts impressive ambient stability (almost no change) after 70 days in an environment with controlled 65% relative humidity, thanks to the superior air stability of the PbS QDs. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) have experienced a rapid progress in terms of efficiency in both single and tandem structures. Herein, two‐terminal (2T) tandem design is fabricated using PV2000:PCBM (1.65 eV) and PM6:Y6 (1.3 eV) blends as bottom and top cells, respectively. The role of transporting and recombination layers on photovoltaic (PV) parameters is studied. The impedance and transmittance results indicate that using SnO2 nanocrystals (NCs) as an electron transporting layer (ETL) in both subcells, the fill factor (FF) and the open circuit voltage (VOC) of the tandem device are increased drastically, mainly due to the lower resistance of the SnO2 layer and its higher transmittance as compared with the ZnO ETL. Moreover, it is found that the VOC and FF losses are reduced using poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Ag (1 nm)/SnO2 NCs as a recombination layer in the tandem design. After proper optimization, a tandem OSC with a VOC of 1.61 V and an efficiency of 14.4% is achieved, which shows great operational stability as well. In addition, the current match and efficiency of the tandem device are increased up to 12.94 mA cm−2 and 15.2%, respectively, by applying a nanotextured anti‐reflection layer on the back of the device. [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.)

Color filters are essential components to realize next‐generation applications based on organic light‐emitting diodes (OLEDs), such as flexible displays and multipurpose lighting. Although the most widely used color filters that include dyes and pigments have advantageous features, such as their simplicity and color purity, the energy wasted by these color filters does not meet the needs for a green and sustainable future. This paper presents a fullerene‐free organic solar cell (OSC) color filter that is not only a highly effective blue color filter, owing to its ability to absorb green and red light, but also functions as an energy‐harvesting device. OLED‐OSC tandem devices with the two distinct functions of OLED and OSC within one device are successfully demonstrated. The OSC of the tandem device generates electrical energy with a power conversion efficiency of 6.83%. The OLED of the tandem device emits blue light with a maximum luminance of 1400 cd m−2, and the International Commission on Illumination (CIE) chromaticity is dramatically tunable from (0.34, 0.36) to (0.14, 0.17). [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskite materials are excellent candidates as light absorbers in tandem solar cells with advantages of tunable bandgaps, high absorption coefficients, facile fabrication processes, and low costs. Tandem devices offer a route to further improve the efficiency and reduce the cost for the solar cell practical applications. One critical challenge that limits the development of two‐terminal perovskite‐based tandem devices is the interconnection between two subcells. To achieve efficient interconnection in the tandem devices, it is required to simultaneously fulfill the high electrical, optical, and chemical requirements. In particular, chemical protection requirement is necessary to enable a tandem device in the case of solution‐processed perovskite–perovskite tandem solar cells. In this work, recent advances of interconnection in perovskite‐based two‐terminal tandem solar cells are reviewed. A brief introduction to the topic is first given. The definition, functions, and requirements of interconnecting layers in two‐terminal tandem devices are then discussed. Next, the insights into recent advances of interconnecting layers in two‐terminal perovskite‐based tandem solar cells (perovskite–perovskite, perovskite–polymer, perovskite–inorganic tandem solar cells) are further described. Finally, an outlook of the future research directions and a brief summary are drawn. [ABSTRACT FROM AUTHOR]

Abstract The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single‐junction and two‐terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single‐junction and two‐terminal tandem NFA‐based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single‐junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10−3 cm2 V−1 s−1 in combination with low nongeminate recombination rate constants of 10−12 cm3 s−1 could lead to PCE values in excess of 20% and 25% for single‐junction and two‐terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single‐junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics.

Perovskite/silicon hybrid tandem solar cells are very close to commercialization owing to their low cost and relatively high efficiency compared to tandem cells based on III-V compound semiconductors. However, most hybrid tandem cell research is based on n-type heterojunction Si cells, which occupy only a small fraction of the total solar market. Here, we propose a new method for optimizing the design of low-cost and high-efficiency monolithic tandem cells based on p-type homojunction Si cells by realizing lossless current matching by simultaneously controlling the band gap energy and thickness of the perovskite film. In addition, systematic studies have been conducted to determine the optimal hole transport layer applicable to the tandem cell from the viewpoint of band alignment and process compatibility, in order to reduce the open-circuit voltage loss. Optimized tandem cells, which were fabricated with a 310 nm thick perovskite layer of (FAPbI 3) 0.8 (MAPbBr 3) 0.2 and a hole transport layer of poly(triaryl amine), had a significantly increased efficiency of 21.19% compared to semi-transparent stand-alone perovskite (13.4%) and Si cells (12.8%). Our tandem cell represented the highest efficiency increment among all monolithic perovskite/Si tandem cells as well as the highest efficiency among monolithic perovskite/Si tandem cells based on p-type homojunction Si cells with Al back-surface fields. The design rules suggested in this study could also be applicable to different types of perovskite/Si tandem cells. Image 1 • A new method for the design of low-cost and high-efficiency monolithic tandem cells based on p-type homojunction Si cells. • Lossless current matching was realized by simultaneously controlling the band gap energy and thickness of the perovskite film. • The optimal hole transport layer has been studied from the viewpoint of band alignment and process compatibility. • The highest efficiency increment among all monolithic perovskite/Si tandem cells. • The highest efficiency among monolithic perovskite/Si tandem cells based on p-type homojunction Si cells with Al-BSF. • The design rules suggested in this study could also be applicable to different types of perovskite/Si tandem cells. [ABSTRACT FROM AUTHOR]

The concept of hybrid tandem device structures that combine metal oxides with thin‐film semiconducting photoabsorbers holds great promise for large‐scale, robust, and cost‐effective bias‐free photoelectrochemical water splitting (PEC‐WS). This work highlights important steps toward the efficient coupling of high‐performance hematite photoanodes with multijunction thin‐film silicon photocathodes providing high bias‐free photocurrent density. The hybrid PEC‐WS device is optimized by testing three types of multijunction silicon photocathodes with the hematite photoanode: amorphous silicon (a‐Si:H) tandem: a‐Si:H/a‐Si:H and triple junction with microcrystalline silicon (μc‐Si:H): a‐Si:H/a‐Si:H/μc‐Si:H and a‐Si:H/μc‐Si:H/μc‐Si:H. The results provide evidence that the multijunction structures offer high flexibility for hybrid tandem devices with regard to tunable photovoltages and spectral matching. Furthermore, both photoanode and photocathode are tested under various electrolyte and light concentration conditions, respectively, with respect to their photoelectrochemical performance and stability. A 27 % enhancement in the solar‐to‐hydrogen conversion efficiency is observed upon concentrating light from 100 to 300 mW cm−2. Ultimately, bias‐free water splitting is demonstrated, with a photocurrent density of 4.6 mA cm−2 (under concentrated illumination) paired with excellent operation stability for more than 24 h of the all‐earth‐abundant and low‐cost hematite/silicon tandem PEC‐WS device. Solar water splitting: An earth‐abundant and low‐cost hematite/silicon tandem hybrid photoelectrochemical water splitting (PEC‐WS) device is investigated. The combination of a nanostructured hematite‐based photoanode with a thin‐film silicon‐based photocathode gives rise to a considerable enhancement in the solar‐to‐hydrogen conversion efficiency as the light is concentrated from 100 to 300 mW cm−2. In addition, a bias‐free water splitting is demonstrated along with excellent operation stability for more than 24 h. [ABSTRACT FROM AUTHOR]

Quantum‐dot light‐emitting diodes (QLEDs) with tandem structures are expected to be one of the candidate technologies for next generation display due to their advantages of high efficiency and long lifetime. In this work, highly efficient tandem red QLEDs with current efficiency (CE) of 44.91 cd/A and external quantum efficiency (EQE) of 30.10 % are successfully demonstrated by using inter‐connecting layer (ICL) based on Al/HATCN/MoO3. The efficiencies are further improved to 51.44 cd/A and 34.4 % by using the liquid metal EGaIn cathode. The developed ICL is stable and reproducible. The demonstrated tandem QLEDs, with high efficiency and long lifetime, would be promising candidates for next generation displays and lighting applications. [ABSTRACT FROM AUTHOR]

Two wide bandgap copolymers based on bulky indacenodithiophene (IDT) and alkoxylated benzothiadiazole units (PIDTBTO-T and PIDTBTO-TT) with the thiophene or thieno[3,2-b]thiophene (TT) π-bridge are designed and synthesized. The effect of π-bridge on the π-π packing, optical, carrier transport, nano-sized phase separation and photovoltaic properties of the copolymers are investigated in depth. In comparison with the PIDTBTO-T-based counterpart, the best performance solar cell based on PIDTBTO-TT exhibits a higher power conversion efficiency (PCE) of 8.15% which is mainly attributed to the formation of a fibrous network for the active layer based on PIDTBTO-TT. Furthermore, when a novel hybrid electron transport layer (PDIN:PFN) is introduced into a tandem solar cell using the PIDTBTO-TT-based device and a PTB7-Th-based device as the bottom and top cell components, respectively, the resulting solar cell exhibits an outstanding PCE of 11.15% with a large open circuit voltage of 1.70 V. To the best of our knowledge, the PCEs of 8.15% and 11.15% are the highest values reported to date for the single-junction and tandem solar cells using IDT-based copolymers, respectively. Our results demonstrate that the π-bridge modulation is effective in adjusting the charge carrier mobility and photovoltaic performance of IDT-based wide bandgap copolymers for single-junction and tandem devices. [ABSTRACT FROM AUTHOR]

Water photolysis is a sustainable technology to convert natural solar energy and water into chemical fuels and is thus considered a thorough solution to the forthcoming energy crises. Unassisted water splitting that could directly harvest solar light and subsequently split water in a single device has become an important research theme. Three types of tandem devices including photoelectrochemical (PEC), photovoltaic (PV) cell/PEC and PV/electrolyser tandem cells are proposed to realize water photolysis at different levels of integration and component. Recent progress in tandem water splitting devices is summarized, and crucial issues on device optimization from the perspective of each photo-absorber functionalities in band edge potential, light absorptivity and transmittance are discussed. By increasing the performances of stand-alone PEC or PV devices, a 20% solar to hydrogen efficiency is predicted that is a significant value towards further application in practice. Accordingly, the challenges for materials development and configuration optimization are further outlined. [ABSTRACT FROM AUTHOR]

In this paper we report the modeling-based design of a CdTe (1.5 eV) on InGaAs (0.74 eV) dual-junction three-terminal solar cell. The device was optimized for thickness of active layers and for doping levels. Efficiency of 26.6% was predicted for the tandem photovoltaic (PV) device under standard testing conditions (STC). We investigated tandem PV device performance at different temperatures and found the device had a total efficiency temperature coefficient of approximately −0.15%/°C. We also investigated device suitability for concentrated photovoltaic (CPV) applications in addition to its conventional PV applications. The device proved a good candidate for CPV applications under 1000 suns. [ABSTRACT FROM AUTHOR]

Water evaporation-induced electricity generation technology has become an extremely interesting issue recently for supplying both freshwater and electricity. This review concentrates on advances in the recent development of water evaporation-induced electricity generation systems for possible application in the Internet of Things, resistive switching memory, devices collecting big data. Additionally, its application in powering some small electronic devices, energy storage, electrochemical deposition and electrochemical cells are also specifically clarified in this work. We divided water evaporation-induced electricity generation systems into three classifications, including tandem devices, hybrid devices, and self-powered generators. The mechanism and application of each electricity generation system are also carefully discussed. Lastly, future opportunities and difficulties to develop water evaporation-induced electricity generation systems are also mentioned. [Display omitted] • Advances in the recent development of light to water evaporation-induced electricity systems have been reviewed. • The ways to improve output power are highlighted. • The mechanism of electricity generation is discussed. • The scalable applications of light to steam-induced electricity systems are discussed. • The crucial challenges in this field are emphasized. [ABSTRACT FROM AUTHOR]

Flexible semitransparent perovskite solar cells (PVSCs) hold promising applications on buildings and unmanned vehicles with irregular surfaces. Efficient wide-bandgap PVSCs are a determining factor for building perovskite-based tandem cells, in which energy level alignment plays significant roles in reducing nonradiative recombination loss at interfaces. Here, we report on the fabrication of efficient flexible semitransparent wide-bandgap PVSCs with gradient energy level alignments at both electron- and hole-selective contacts. We design a triple-electron-selective contact as electron transport layers with gradient Fermi level alignment with the conduction band of wide-bandgap perovskite, which consists of trans-1,2-Diaminocyclohexane-N,N,N′,N′-tetraacetic (CyDTA), tin dioxide (SnO 2), and CyDTA-complexed SnO 2. Moreover, an ultrathin gold layer embedded between 2,2′,7,7′-tetrakis(N,N-bis(p-methoxy-phenyl)amino)-9,9′-spirobifluorene (spiro-OMeTAD) hole transport layer and molybdenum oxide protection layer facilitates effective hole transport to the anode. We conduct comprehensive and solid simulation at both charge-selective contacts to reveal the working mechanisms. The champion flexible semitransparent 1.75 eV wide-bandgap PVSC achieves an efficiency of 15.02% with excellent light transparency of around 70% beyond the wavelength of 700 nm, enabling all-flexible perovskite/Cu(In,Ga)Se 2 tandem devices with efficiencies beyond 21%. Image 1 • Efficient flexible semitransparent perovskite solar cells are achieved with a gradient energy level strategy. • A triple-layer electron-selective contact of CyDTA/SnO 2 /C-SnO 2 benefits energy level matching with wide-bandgap perovskite. • An ultrathin gold layer facilitates effective hole transport to the transparent anode. • Comprehensive simulation at both charge-selective contacts uncovers the working mechanisms. • This is the first demonstration of efficient four-terminal all-flexible perovskite/Cu(In,Ga)Se 2 tandem device. [ABSTRACT FROM AUTHOR]

Semitransparent solar cells (ST-SCs) have received great attention due to their promising application in many areas, such as building integrated photovoltaics (BIPVs), tandem devices, and wearable electronics. In the past decade, perovskite solar cells (PSCs) have revolutionized the field of photovoltaics (PVs) with their high efficiencies and facile preparation processes. Due to their large absorption coefficient and bandgap tunability, perovskites offer new opportunities to ST-SCs. Here, a general overview is provided on the recent advances in ST-PSCs from materials and devices to applications and some personal perspectives on the future development of ST-PSCs., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single‐junction and two‐terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single‐junction and two‐terminal tandem NFA‐based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single‐junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10−3 cm2 V−1 s−1 in combination with low nongeminate recombination rate constants of 10−12 cm3 s−1 could lead to PCE values in excess of 20% and 25% for single‐junction and two‐terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single‐junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics. [ABSTRACT FROM AUTHOR]

The tandem structure is an efficient way to simultaneously tackle absorption and thermalization losses of the single junction solar cells. In this work, a high-performance tandem organic solar cell (OSC) using two subcells with the same donor poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] (PBDB-T) and two acceptors, F-M and 2,9-bis(2-methylene-(3(1,1-dicyanomethylene)benz[f ]indanone))7,12-dihydro-(4,4,10,10-tetrakis(4-hexylphenyl)-5,11-diocthylthieno[3',2':4,5]cyclopenta[1,2-b]thieno[2″,3″:3',4']cyclopenta[1',2':4,5]thieno[2,3-f][1]benzothiophene (NNBDT), with complementary absorptions is demonstrated. The two subcells show high V oc with value of 0.99 V for the front cell and 0.86 V for the rear cell, which is the prerequisite for obtaining high V oc of their series-connected tandem device. Although there is much absorption overlap for the subcells, a decent J sc of the tandem cell is still obtained owing to the complementary absorption of the two acceptors in a wide range. With systematic device optimizations, a best power conversion efficiency of 14.52% is achieved for the tandem device, with a high V oc of 1.82 V, a notable FF of 74.7%, and a decent J sc of 10.68 mA cm -2 . This work demonstrates a promising strategy of fabricating high-efficiency tandem OSCs through elaborate selection of the active layer materials in each subcell and tradeoff of the V oc and J sc of the tandem cells., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Solar photon-to-electron conversion with polymer solar cells (PSCs) has experienced rapid development in the recent few years. Even so, the exploration of molecules and devices in efficiently converting near-infrared (NIR) photons into electrons remains critical, yet challenging. Herein presented is a family of near-infrared nonfullerene acceptors (NIR NFAs, T1-T4) with fluorinated regioisomeric A-Aπ-D-Aπ-A backbones for constructing efficient single-junction and tandem PSCs with photon response up to 1000 nm. It is found that the tuning of the regioisomeric bridge (Aπ) and fluoro (F)-substituents on a molecular skeleton strongly influences the backbone conformation and conjugation, leading to the optimized optoelectronic and stable stacking of resultant NFAs, which eventually impacts the performance of derived PSCs. In PSCs, the proximal NFAs with varied F-atoms (T1-T3) mostly outperform than that of distal NFA (T4). Notably, single-junction PSC with PTB7-Th:T2 blend can reach 10.87% power conversion efficiency (PCE), after implementing a solvent additive to improve blend morphology. Moreover, efficient tandem PSCs are fabricated through integrating such NIR cells with mediate bandgap nonfullerene-based subcells, to achieve a PCE of 14.64%. The results reveal the structural design of organic semiconductor and device with improved photovoltaic performance., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Highly efficient polymer solar cells with a tandem structure are fabricated by using two excellent photovoltaic polymers and a highly transparent intermediate recombination layer. Power conversion -efficiencies over 10% can be realized with a photovoltaic response within 800 nm., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)