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Triplet materials are designed by introducing heavy atoms to enhance spin–orbit coupling or constructing donor and acceptor units with a twisted conformation to reduce ΔE _ST. However, the twisted materials have not been applied in solar cells due to weak absorption and low charge‐transport mobilities. Now two nonplanar acceptors with large π‐conjugated core were constructed that achieved over 15 % efficiency.

Abstract

Triplet acceptors have been developed to construct high‐performance organic solar cells (OSCs) as the long lifetime and diffusion range of triplet excitons may dissociate into free charges instead of net recombination when the energy levels of the lowest triplet state (T₁) are close to those of charge‐transfer states (³CT). The current triplet acceptors were designed by introducing heavy atoms to enhance the intersystem crossing, limiting their applications. Herein, two twisted acceptors without heavy atoms, analogues of Y6, constructed with large π‐conjugated core and D‐A structure, were confirmed to be triplet materials, leading to high‐performance OSCs. The mechanism of triplet excitons were investigated to show that the twisted and D‐A structures result in large spin–orbit coupling (SOC) and small energy gap between the singlet and triplet states, and thus efficient intersystem crossing. Moreover, the energy level of T₁ is close to ³CT, facilitating the split of triplet exciton to free charges.

Herein, large‐area silicon heterojunction solar cells with efficiency of 22.0% using commercial‐grade p‐type Czochralski silicon wafers are demonstrated. An advanced hydrogenation process is developed to overcome the impact of boron–oxygen light‐induced degradation in these p‐type cells, resulting in stable V _OC of 736 mV. This can be a potential pathway to lower cost high‐efficiency solar cells.

Herein, large‐area defect‐engineered p‐type silicon heterojunction (SHJ) solar cells using standard 1.6 Ω cm commercial‐grade boron‐doped Czochralski (Cz) silicon wafers are fabricated. It is demonstrated that despite achieving an open‐circuit voltage of 735 mV with an efficiency of 21.6% for gettered samples, without appropriate treatment, the cells are heavily susceptible to boron–oxygen‐related light‐induced degradation (LID), with the effective lifetime at maximum power point decreasing to 13 μs. This degradation results in a loss of efficiency of more than 3.1%_abs (14.3%_rel) after 48 h of light soaking. However, the addition of an advanced hydrogenation postcell fabrication process increases the efficiency by 0.2%_abs to 21.8%, and dramatically reduces susceptibility of LID, decreasing the extent of degradation to 0.2%_abs (0.9%_rel). A peak stable independently measured efficiency of 22.0% with an open‐circuit voltage (V _OC) of 736 mV is achieved with the addition of a dedicated high‐temperature prefabrication hydrogenation. These results indicate that p‐type Cz wafers can be used to fabricate stable, next‐generation high‐efficiency solar cells using silicon heterojunctions or other passivated contact architectures requiring V _OCS well above 700 mV.

The nonionic polymer with multiple amino groups is introduced to passivate both metal‐ and halide‐induced defects of all‐inorganic CsPbI₂Br perovskite by coordination and hydrogen bonds, simultaneously. Consequently, a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film are achieved, which boosts the efficiency of perovskite solar cells up to 15.48% with excellent humidity stability.

The all‐inorganic CsPbI₂Br perovskite with superior thermal durability faces challenges of low‐phase stability and high moisture sensitivity. Herein, a nonionic additive of polyethyleneimine (PEI) with multiple amino groups is introduced to form hydrogen bond with I⁻/Br⁻ ions and coordinate with Pb²⁺/Cs⁺ ions simultaneously. The strong interplay between PEI and CsPbI₂Br achieves a well‐controlled grain size, reduced defects, and reinforced phase structure of CsPbI₂Br film, which boosts the power conversion efficiency (PCE) of perovskite solar cells to 15.48%. The hydrophobic long alkyl chain of PEI greatly improves the humidity resistance, retaining 81.9% of initial PCE of zjr unsealed device under 20 ± 5% relative humidity (RH) for 500 h. Remarkably, a PCE of 13.37% is achieved by the device based on CsPbI₂Br–PEI film processed under ambient condition (≈22% RH, ≈25 °C).

Post‐treating the mesoporous TiO₂/ZrO₂/carbon triple layer by alkali metal sulfonate compounds enables a significantly enhanced photovoltage for hole‐conductor‐free printable mesoscopic perovskite solar cells. The devices demonstrate high operational stability, retaining 91.7% of their initial efficiency after 1000 h continuous operation at the maximum power point under 1 sun illumination.

Triple‐mesoscopic perovskite solar cells (PSCs) based on TiO₂/ZrO₂/carbon architecture have attracted much attention due to their excellent long‐term stability and screen‐printing technique‐based fabrication process. However, the relatively low open‐circuit voltage (V _OC) limits the further improvement of power conversion efficiency (PCE) for triple‐mesoscopic PSCs. Herein, 2‐phenyl‐5‐benzimidazole sulfonate‐Na to post‐treat the triple‐mesoscopic structured scaffold is introduced. The conduction band of the mesoporous TiO₂ layer (electron transport layer [ETL]) is significantly shifted up from −4.22 to −4.11 eV, which favors the electron transfer from the perovskite absorber to the ETL. At the same time, the recombination at the interface of ETL/perovskite is effectively suppressed. Correspondingly, the V _OC and fill factor (FF) of the devices are enhanced without sacrificing the photocurrent density (J _SC). With optimal post‐treatment conditions, the champion device delivers a V _OC of 1.02 V and an FF of 0.70 with J _SC of 23.06 mA cm⁻², showing an overall PCE of 16.51%. After 1000 h continuous operation at the maximum power point under AM1.5G 1 sun illumination, the devices can maintain 91.7% of the initial efficiency. This simple procedure and significant photovoltage enhancement render this method promising for fabricating efficient PSCs based on mesoporous charge transport layers.

Hole‐Transporting Materials

In article number 2000109, Zong‐Xiang Xu and co‐workers determine that the highest power conversion efficiency of perovskite solar cells based on a poly(3‐hexylthiophene)/gold nanorod (P3HT/AuNR) composite hole‐transporting material reaches up to 16.88%, which is an increase of 26% from that of a pristine P3HT‐based device (13.40%). The enhanced performance is attributed to the higher carrier mobility and increased light utilization efficiency induced by the addition of AuNRs with localized surface plasmon resonance effect in the polymer matrix.

Passivation Agents

In article number 2000082, Fei Zhang, Kai Zhu, and co‐workers design a more efficient and stable perovskite solar cell by partially replacing phenylethylammonium (PEA⁺) with pentauorophenethylammonium (F5PEA⁺) as the 2D perovskite passivation agent by forming a strong noncovalent interaction between the two bulky cations, which enhances charge transport, and presents the highest performance for reported wide‐bandgap perovskite solar cells.

Perovskite Solar Cells

In article number 2000093, Ming‐Chung Wu, Kun‐Mu Lee, and co‐workers use polyethylene glycol (PEG) as an additive for the perovskite active layer in lead‐reduced perovskite solar cells. The PEG can effectively control the surface morphology of the perovskite film and improve the charge carrier transport. For 10% lead‐reduced perovskite solar cells, a champion power conversion effi ciency of 16.1% is obtained without signifi cant hysteresis.

Perovskite Solar Cells

In article number 2000001, Jingjing Chang and co‐workers demonstrate a novel approach where a short‐period deep‐ultraviolet (DUV) photoactivation process is employed to modify SnO₂ electron transport layers to achieve all‐inorganic perovskite solar cells with high efficiency exceeding 15% with good stability. The DUV treatment induces better energy level alignment, more ordered crystal growth, and reduces interface stress related defects.

The surface and bulk defects of perovskite films are simultaneously passivated through the treatment of CsBr/methanol solution, in which the methanol helps CsBr penetrate the depth of the perovskite and reconstruct high‐quality films. This strategy can effectively improve the photovoltaic performance and operational stability of the resultant devices.

It is challenging to passivate defects that are buried in the depth of perovskite films; most of the reported passivation methods cannot reach the deep defects. Herein, methanol is adopted as a dual‐functional reagent to not only act as a solvent but also help the dissolved ions penetrate the depth of perovskite films. By treating the as‐prepared perovskite films with CsBr/methanol solution, Br⁻ ions can react with the undercoordinated Pb²⁺, and Cs⁺ ions can fill in the cation vacancies. This strategy enables surface and bulk defects passivation to be achieved simultaneously. The nonradiative recombination of the double‐passivated devices is significantly suppressed and the migration of charged defects is remarkably hindered. As a result, an improved power conversion efficiency of 19.5% and an open‐circuit voltage of 1.183 V is achieved. Moreover, the passivated device can retain ≈80% of the initial efficiency after working for 500 h at maximum power point under 1‐sun illumination, whereas the pristine device reaches 80% of the initial efficiency after only 90 h. This work demonstrates that surface and bulk defects passivation is critical to improve the efficiency and long‐term operational stability of the perovskite solar cells.

A formamidinium derivative, 2‐thiopheneformamidinium (ThFA), is successfully developed and used as a spacer in 2D RP perovskite (ThFA)₂MA _{n −1}Pb _n I_{3 n +1} (nominal n = 3). A precursor organic salts‐assisted crystal growth technique is further developed to prepare high‐quality 2D RP perovskite films, resulting in a high power conversion efficiency of 16.72% with negligible hysteresis and improved stability.

Abstract

Formamidinium (FA)‐based 3D perovskite solar cells (PSCs) have been widely studied and they show reduced bandgap, enhanced stability, and improved efficiency compared to MAPbI₃‐based devices. Nevertheless, the FA‐based spacers have rarely been studied for 2D Ruddlesden–Popper (RP) perovskites, which have drawn wide attention due to their enormous potential for fabricating efficient and stable photovoltaic devices. Here, for the first time, FA‐based derivative, 2‐thiopheneformamidinium (ThFA), is successfully synthesized and employed as an organic spacer for 2D RP PSCs. A precursor organic salts‐assisted crystal growth technique is further developed to prepare high quality 2D (ThFA)₂(MA) _{n −1}Pb _n I_{3 n +1} (nominal n = 3) perovskite films, which shows preferential vertical growth orientations, high charge carrier mobilities, and reduced trap density. As a result, the 2D RP PSCs with an inverted planar p‐i‐n structure exhibit a dramatically improved power conversion efficiency (PCE) from 7.23% to 16.72% with negligible hysteresis, which is among the highest PCE in 2D RP PSCs with low nominal n‐value of 3. Importantly, the optimized 2D PSCs exhibit a dramatically improved stability with less than 1% degradation after storage in N₂ for 3000 h without encapsulation. These findings provide an effective strategy for developing FA‐based organic spacers toward highly efficient and stable 2D PSCs.

Intensity‐dependent absolute photoluminescence studies on perovskite neat materials and partial cell stacks highlight how interface recombination can account for ideality factors between 1 and 2, commonly observed in perovskite devices. The findings are rationalized via a recombination model which details how interface recombination can lead to ideality factors of unity, in this case, not representative of a better device.

Abstract

The measurement of the ideality factor (n _id) is a popular tool to infer the dominant recombination type in perovskite solar cells (PSC). However, the true meaning of its values is often misinterpreted in complex multilayered devices such as PSC. In this work, the effects of bulk and interface recombination on the n _id are investigated experimentally and theoretically. By coupling intensity‐dependent quasi‐Fermi level splitting measurements with drift diffusion simulations of complete devices and partial cell stacks, it is shown that interfacial recombination leads to a lower n _id compared to Shockley–Read–Hall (SRH) recombination in the bulk. As such, the strongest recombination channel determines the n _id of the complete cell. An analytical approach is used to rationalize that n _id values between 1 and 2 can originate exclusively from a single recombination process. By expanding the study over a wide range of the interfacial energy offsets and interfacial recombination velocities, it is shown that an ideality factor of nearly 1 is usually indicative of strong first‐order non‐radiative interface recombination and that it correlates with a lower device performance. It is only when interface recombination is largely suppressed and bulk SRH recombination dominates that a small n _id is again desirable.

In article number https://doi.org/10.1002/adfm.2020015572001557, Wei Wang, Zongping Shao, and co‐workers introduce a multifunctional dye interlayer into lead‐free all‐inorganic Cs₂AgBiBr₆‐based perovskite solar cells to enhance the efficiency and stability by broadening the absorption spectrum, accelerating the charge carrier extraction, and constructing an appropriate energy level alignment. Consequently, the modified device delivers a higher power conversion efficiency of 2.84% and better stability under ambient conditions. Cover illustrator: Xiaoqing Yang.

A secondary bond‐constructed isotropic electron transfer 3D‐network is fabricated based on biomass‐derived demethylated kraft lignin (D_MeKL). Secondary bonds successfully modify the contact of the perylene diiminde/active layer and conjugate‐blocked linkages in D_MeKL, to overcome anisotropy‐aroused electron transfer barriers at the cathode interface. The enhancement of cross/vertical‐sectional electron transfer performance and well‐matched energy levels yields the highest power conversion efficiency reported among biomaterial‐based organic solar cells.

Abstract

Fabricating high‐efficient electron transporting interfacial layers (ETLs) with isotropic features is highly desired for all‐directional electron transfer/collection from an anisotropic active layer, achieving excellent power conversion efficiency (PCEs) on nonfullerene acceptor (NFA) organic solar cells (OSCs). The complicated synthesis and cost‐consumption in exploring versatile materials arouse great interest in the development of binary‐doping interlayers without phase separation and flexible manipulation. Herein, for the first time, a novel cathode interfacial layer based on biomass‐derived demethylated kraft lignin (D_MeKL) is proposed. Features of multiple phenolic‐hydroxyl (PhOH) and uniform‐distributed render D_MeKL to exhibit an excellent bonding capacity with amino terminal substituted perylene diiminde (PDIN), and successfully form a high‐efficient isotropic electron transfer 3D network. Synchronously, secondary bonds completely modify conjugate‐blocked linkages of D_MeKL, significantly enhance the electron transporting performance on cross‐section and vertical‐sections, and repair the contact of PDIN with active layer. The D_MeKL/PDIN‐based 3D‐network exhibits well‐matched work function (WF) (–4.34 eV) with cathode (–4.30 eV) and energy level of electron acceptor (–4.11 eV). D_MeKL/PDIN‐based NFAs‐OSC shows excellent short‐circuit current density (26.61 mA cm^–2) and PCE (16.02%) beyond the classic PDIN‐based NFA‐OSC (25.64 mA cm^–2, 15.41%), which is the highest PCEs among biomaterials interlayers. The results supply a novel method to achieve high‐efficient cathode interlayer for NFAs‐OSCs.

Lead‐based halide perovskites are toxic and exhibit poor environmental stability. Herein, a thin‐film and optoelectronic device consisting of barium zirconium sulfide (BaZrS₃)—a lead‐free chalcogenide perovskite—are reported. Experiments and simulations demonstrate that BaZrS₃ is intrinsically more stable than organic–inorganic halide perovskites such as methylammonium lead iodide. The findings highlight the potential of chalcogenide perovskites for optoelectronic and thermoelectric applications.

Abstract

Organic–inorganic halide perovskites are intrinsically unstable when exposed to moisture and/or light. Additionally, the presence of lead in many perovskites raises toxicity concerns. Herein, a thin film of barium zirconium sulfide (BaZrS₃), a lead‐free chalcogenide perovskite, is reported. Photoluminescence and X‐ray diffraction measurements show that BaZrS₃ is far more stable than methylammonium lead iodide (MAPbI₃) in moist environments. Moisture‐ and light‐induced degradations in BaZrS₃ and MAPbI₃ are compared by using simulations and calculations based on density functional theory. The simulations reveal drastically slower degradation in BaZrS₃ due to two factors—weak interaction with water and very low rates of ion migration. BaZrS₃ photodetecting devices with photoresponsivity of ≈46.5 mA W⁻¹ are also reported. The devices retain ≈60% of their initial photoresponse after 4 weeks under ambient conditions. Similar MAPbI₃ devices degrade rapidly and show a ≈95% decrease in photoresponsivity in just 4 days. The findings establish the superior stability of BaZrS₃ and strengthen the case for its use in optoelectronics. New possibilities for thermoelectric energy conversion using these materials are also demonstrated.

In article number https://doi.org/10.1002/adfm.2020014942001494, Lihui Chen, Xinhua Ouyang, and co‐workers successfully demonstrate secondary bonds to modify conjugate‐blocked linkages of biomass‐derived lignin or the electron transfer layer of organic solar cells. The enhanced conductivity, resisted phase separation, and repaired the contact makes it valuable for organic electronics.

In article number https://doi.org/10.1002/adfm.2020015572001557, Wei Wang, Zongping Shao, and co‐workers introduce a multifunctional dye interlayer into lead‐free all‐inorganic Cs₂AgBiBr₆‐based perovskite solar cells to enhance the efficiency and stability by broadening the absorption spectrum, accelerating the charge carrier extraction, and constructing an appropriate energy level alignment. Consequently, the modified device delivers a higher power conversion efficiency of 2.84% and better stability under ambient conditions. Cover illustrator: Xiaoqing Yang.

A multifunctional N719 dye interlayer is introduced into lead‐free all‐inorganic Cs₂AgBiBr₆‐based perovskite solar cells to enhance the efficiency and stability by broadening the absorption spectrum, promoting the charge carrier separation/extraction and constructing an appropriate energy level alignment. As a result, the optimized device shows a superior power conversion efficiency of 2.84% and excellent operational stability under ambient conditions.

Abstract

Perovskite solar cells (PSCs) are highly promising next‐generation photovoltaic devices because of the cheap raw materials, ideal band gap of ≈1.5 eV, broad absorption range, and high absorption coefficient. Although lead‐based inorganic‐organic PSC has achieved the highest power conversion efficiency (PCE) of 25.2%, the toxic nature of lead and poor stability strongly limits the commercialization. Lead‐free inorganic PSCs are potential alternatives to toxic and unstable organic‐inorganic PSCs. Particularly, double‐perovskite Cs₂AgBiBr₆‐based PSC has received interests for its all inorganic and lead‐free features. However, the PCE is limited by the inherent and extrinsic defects of Cs₂AgBiBr₆ films. Herein, an effective and facile strategy is reported for improving the PCE and stability by introducing an N719 dye interlayer, which plays multifunctional roles such as broadening the absorption spectrum, suppressing the charge carrier recombination, accelerating the hole extraction, and constructing an appropriate energy level alignment. Consequently, the optimizing cell delivers an outstanding PCE of 2.84%, much improved as compared with other Cs₂AgBiBr₆‐based PSCs reported so far in the literature. Moreover, the N719 interlayer greatly enhances the stability of PSCs under ambient conditions. This work highlights a useful strategy to boost the PCE and stability of lead‐free Cs₂AgBiBr₆‐based PSCs simultaneously, accelerating the commercialization of PSC technology.

In article number https://doi.org/10.1002/adfm.2020015572001557, Wei Wang, Zongping Shao, and co‐workers introduce a multifunctional dye interlayer into lead‐free all‐inorganic Cs₂AgBiBr₆‐based perovskite solar cells to enhance the efficiency and stability by broadening the absorption spectrum, accelerating the charge carrier extraction, and constructing an appropriate energy level alignment. Consequently, the modified device delivers a higher power conversion efficiency of 2.84% and better stability under ambient conditions. Cover illustrator: Xiaoqing Yang.

Dramatically boosted device performance is observed from perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films, which possesses superior film morphology, boosted and balanced charge carrier mobility, suppressed trap density and charge carrier recombination, and promoted charge carrier extraction time.

Abstract

Perovskite photovoltaics have drawn great attention in both academic and industrial sectors in the past decade. To date, impressive device performance has been achieved in state‐of‐the‐art device architectures through morphological manipulation and generic interface engineering. In this study, enhanced device performance of perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃‐mixed Fe₃O₄ magnetic nanoparticles (CH₃NH₃PbI₃:Fe₃O₄) composite thin films is reported. It is found that magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films possess superior film morphology, boosted and balanced charge carrier mobility, and suppressed trap density. Moreover, perovskite photovoltaics by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit suppressed charge carrier recombination and shorter charge carrier extraction time. As a result, perovskite solar cells by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit 20.23% power conversion efficiency with significantly reduced photocurrent hysteresis. Moreover, perovskite photodetectors by magnetic field‐aligned CH₃NH₃PbI₃:Fe₃O₄ composite thin films exhibit a photoresponsivity of 858 mA W⁻¹, a photodetectivity over 10¹³ Jones (1 Jones = 1 cm Hz^1/2 W⁻¹) and a linear dynamic range over 160 dB at room temperature. All these device performance parameters are significantly better than those by pristine CH₃NH₃PbI₃ thin film. Thus, these studies provide a facile way to boost device performance of perovskite photovoltaics.

A simple yet efficient hybrid photorechargeable design is presented, which consists of a monolithic integration of perovskite solar cell and lithium ion battery enabled by an electronic converter and demonstrates an overall photoelectric conversion‐storage efficiency of 7.3%.

Abstract

Photovoltaic power‐conversion systems can harvest energy from sunlight almost perpetually whenever sunrays are accessible. Meanwhile, as indispensable energy storage units used in advanced technologies such as portable electronics, electric vehicles, and renewable/smart grids, batteries are energy‐limited closed systems and require constant recharging. Fusing these two essential technologies into a single device would create a sustainable power source. Here, it is demonstrated that such an integrated device can be realized by fusing a rear‐illuminated single‐junction perovskite solar cell with Li₄Ti₅O₁₂‐LiCoO₂ Li‐ion batteries, whose photocharging is enabled by an electronic converter via voltage matching. This design facilitates a straightforward monolithic stacking of the battery on the solar cell using a common metal substrate, which provides a robust mechanical isolation between the two systems while simultaneously providing an efficient electrical interconnection. This system delivers a high overall photoelectric conversion‐storage efficiency of 7.3%, outperforming previous efforts on stackable integrated architectures with organic–inorganic photovoltaics. Furthermore, converter electronics facilitates system control with battery management and maximum power point tracking, which are inevitable for efficient, safe, and reliable operation of practical loads. This work presents a significant advancement toward integrated photorechargeable energy storage systems as next‐generation power sources.

Impact of encapsulation on performance and stability of organic solar cell is studied. Delaminations produced during R2R process induce an important performance loss and a weak stability in temperature or/and humidity.

Abstract

To increase the lifetime of organic photovoltaic (OPV) devices and pass European lifetime standards, some encapsulation systems are often used to limit the exposition to oxygen and humidity of solar cells. Despite this progress, the damages induced by the encapsulation process are scarcely studied in literature. In this article, the consequences of the common roll‐to‐roll and vacuum lamination approaches are investigated and compared. The losses of performances are first followed induced by both the encapsulation itself and in a damp heat ageing. The vacuum lamination seems harmless for the solar cells. However, a significant damage is evidenced, even with a relatively mild roll‐to‐roll encapsulation. The degradation mechanisms are further investigated by complementary imaging characterization tools: photoluminescence/electroluminescence imaging and spectroscopy, laser‐beam‐induced current mapping, and correlated to J(V) curves. The recent advancements in the optoelectronic domain may allow linking cell performance to localized flaws. It appears that, although the processing conditions are rather homogeneous, the resulting degradation ends up with a strong localization feature.