Yingzhi Jin

A power conversion efficiency of 17.61% is achieved in organic photovoltaic devices (OPVs) with D18-Cl:PM6:Y6 as active layers. The good compatibility and similar highest occupied molecular orbital levels of D18-Cl and PM6 enable the formation of an alloyed state for efficient hole transport. Energy ransfer from D18-Cl to PM6 should improve the exciton utilization in ternary blend OPVs.

Efficient ternary blend organic photovoltaic devices (OPVs) are built based on a D18-Cl:Y6 host system and star polymer donor PM6 as the third component. A power conversion efficiency (PCE) of 16.89% is achieved in D18-Cl:Y6 host binary OPVs, with a short-circuit current density (J _SC) of 25.31 mA cm⁻², an open-circuit voltage (V _OC) of 0.878 V, and a fill factor (FF) of 75.81%. Upon incorporating appropriate PM6 in active layers, the PCE of optimal ternary blend OPVs can be increased to 17.61%, benefiting from a J _SC of 26.35 mA cm⁻², a V _OC of 0.871 V, and an FF of 76.82%. Polymers D18-Cl and PM6 have good compatibility and similar highest occupied molecular orbital (HOMO) levels, which enable to form D18-Cl:PM6 alloyed states for efficient hole transport in ternary blend active layers. Meanwhile, trap density in ternary blend active layers is decreased by incorporating PM6, which is conducive to weaken charge recombination in ternary blend active layers. The gradually varied V _OC values of ternary blend OPVs can be well explained from the varied HOMO levels of D18-Cl:PM6 alloyed states. The results indicate that two compatible polymer donors with similar HOMO levels have great potential in achieving efficient ternary blend OPVs.

We constructed a series of noncovalently fused-ring electron acceptors (NFREAs) with S⋅⋅⋅O noncovalent intramolecular interactions. Combining the strategies of noncovalent conformational locks and π-extended end-group engineering, a record PCE of 14.53 % in labs and a certified PCE of 13.8 % for NFREAs based devices were achieved.

Abstract

Noncovalently fused-ring electron acceptors (NFREAs) have attracted much attention in recent years owing to their advantages of simple synthetic routes, high yields and low costs. However, the efficiencies of NFREAs based organic solar cells (OSCs) are still far behind those of fused-ring electron acceptors (FREAs). Herein, a series of NFREAs with S⋅⋅⋅O noncovalent intramolecular interactions were designed and synthesized with a two-step synthetic route. Upon introducing π-extended end-groups into the backbones, the electronic properties, charge transport, film morphology, and energy loss were precisely tuned by fine-tuning the degree of multi-fluorination. As a result, a record PCE of 14.53 % in labs and a certified PCE of 13.8 % for NFREAs based devices were obtained. This contribution demonstrated that combining the strategies of noncovalent conformational locks and π-extended end-group engineering is a simple and effective way to explore high-performance NFREAs.

Benefiting from the correlations that reducing the active layer thickness can greatly enhance its resistance to thermal stress and improve the photo-thermal stability of highly efficient organic photovoltaic systems, a new i-FOM model (i.e., i-FoM2.0) is introduced as a more effective and rational guideline for verifying the true potential of next-generation organic photovoltaic systems. Of note is that this work provides a promising trade-off strategy for reducing efficiency-stability-cost gap and accelerates the commercialization of organic solar cells.

A new high-performance indoor non-fullerene acceptor with a desirable optical band gap, named FCC-Cl, was developed by combining a weak electron-donating core and a moderate electron-withdrawing end group. The FCC-Cl-based devices achieved a record indoor power conversion efficiency of 28.8% at 2600K LED at 500 lux due to the well-matched absorption spectrum, high crystallinity, and high absorption coefficient of FCC-Cl. Our work provides guidelines for efficient materials toward high-performance indoor OPVs and proves the feasibility of practical applications of indoor OPVs.

The organic molecule 3-phosphonopropionic acid (H3pp) interacts strongly with the halide perovskite through two types of hydrogen bonds (H…I and O…H). This binding mode results in shallow point defect passivation that has a significant impact on the perovskite solar cell stability but not on the no-radiative recombination and device efficiency. Our method permits to obtain highly efficient, >21%, PSCs with outstanding operational stability, retaining nearly 100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5 illumination.

In this work, we demonstrate the critical importance of the following: (1) temporal stability and spatial homogeneity of the light sources, (2) calibration of the spectral irradiance and illuminations of the light sources, (3) the area of the cells, (4) the aperture of the mask, and (5) stray lights from the measurement environment. We suggest a practical approach to reliably evaluating the power-conversion efficiencies of photovoltaic cells for indoor applications.

The main role of triplets as a solar cell efficiency loss mechanism in DRCN5T systems is elucidated. Despite the high efficiencies obtained with DRCN5T, it creates a considerable large number of triplets. It is also found that these triplets decrease the charge population through triplet-charge annihilation. Moreover, a method is proposed to probe this process present in fullerene and non-fullerene blends.

Abstract

Organic photovoltaics (OPV) are close to reaching a landmark 20% device efficiency. One of the proposed reasons that OPVs have yet to attain this milestone is their propensity toward triplet formation. Herein, a small molecule donor, DRCN5T, is studied using a variety of morphology and spectroscopy techniques, and blended with both fullerene and non-fullerene acceptors. Specifically, grazing incidence wide-angle X-ray scattering and transient absorption, Raman, and electron paramagnetic resonance spectroscopies are focused on. It is shown that despite DRCN5T's ability to achieve OPV efficiencies of over 10%, it generates an unusually high population of triplets. These triplets are primarily formed in amorphous regions via back recombination from a charge transfer state, and also undergo triplet-charge annihilation. As such, triplets have a dual role in DRCN5T device efficiency suppression: they both hinder free charge carrier formation and annihilate those free charges that do form. Using microsecond transient absorption spectroscopy under oxygen conditions, this triplet-charge annihilation (TCA) is directly observed as a general phenomenon in a variety of DRCN5T: fullerene and non-fullerene blends. Since TCA is usually inferred rather than directly observed, it is demonstrated that this technique is a reliable method to establish the presence of TCA.

An alternative pathway to the determination of organic solar cell fill-factor figures of merit, θ and α, expressing them in terms of the effective carrier drift and diffusion lengths is presented. This simplifies their elucidation with the experimental results, covering a range of nonfullerene acceptor-based devices, demonstrating a strong agreement both with the analytical equations and the drift-diffusion simulations.

Abstract

Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open-circuit voltage loss and fill-factor, with state-of-the-art OSCs rarely displaying fill-factor of 80% and above. The fill-factor of transport-limited solar cells, including organic photovoltaic devices, is affected by material and device-specific parameters, whose combination is represented in terms of the established figures of merit, such as θ and α. Herein, it is demonstrated that these figures of merit are closely related to the long-range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady-state photoconductance measurements. This yields a straightforward way of determining θ and α in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices—including the high efficiency nonfullerene acceptor blends—and show that the diffusion length of the free carriers provides a good correlation with the fill-factor. It is, finally, concluded that most state-of-the-art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor.

17.10% efficiency for PM6: Y6-based devices is gained by finely tuning the interface morphology through poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) doping engineering. A comprehensive comparison of dopant solubility affected compatibility with photoactive systems is described. One of the highest efficiencies (15.62%) for all-polymer solar cells is enabled by the dopants.

Abstract

Anode modification is vital for improving device performance of organic solar cells (OSCs). PEDOT:PSS is the most widely applied hole transport layer (HTL) in OSCs. In this work, three kinds of modified HTLs, namely PEDOT:PSS-PA, PEDOT:PSS-TA, and PEDOT:PSS-DA are readily prepared via simple doping of phenylethylamine derivatives into commercially available Al 4083, by modulating the number of hydroxyl groups on the adulterant molecules. All of them exhibit enhanced work functions (WFs) and conductivities. Matching with PM6:Y6 composed active layers, PEDOT:PSS-TA based devices achieves the highest performance with a power conversion efficiency (PCE) of 17.10%, while the PM6:ITC-2Cl system demonstrates a highest PCE of 14.17% in devices with PEDOT:PSS-DA, and the optimal PCE of PM6:PIDTC-T based OSCs is equal to 9.55% while the HTL is PEDOT:PSS-PA. Further investigations reveal that the different adulterants formed various amount of hydrogen bonds in HTLs, inducing dissimilar interfacial morphology and mobility, and thus unidentical degrees of change in recombination. Afterwards, the doping strategy is extended to a newly proposed high-performance system PM6:PY-IT, and successfully drags its efficiency from 14.78% to 15.62%, another world-class breakthrough for all-polymer solar cells. In summary, this study not only achieves a series of OSCs with improved PCEs, but also delivers a deep understanding of PEDOT:PSS improvement.

Perovskite/Silicon tandem solar cells (PK/c-Si tandem) offer a promising path for breaking the Shockley-Queisser limit of single junction cells. However, the efficiency of PK/c-Si tandems is still below the theoretical limit. Here, the detailed constraints on efficiency, stability, costs, and large-scale preparation of this technology are discussed, some corresponding solutions are proposed to further promote its development.

Abstract

In recent years, perovskite/silicon tandem solar cells (PK/c-Si tandem) have demonstrated high power conversion efficiency (PCE) and demonstrated great application potential in photovoltaic (PV) systems. However, the PCE of PK/c-Si tandem devices is still below the theoretical limit. From a broader perspective, their poor stability and difficulty in large-area realization are crucial barriers for commercial viability. In this report, the detailed constraints facing high PCE of tandem devices and the corresponding solutions are discussed. The authors propose that the main obstacle comes from the limitation of the perovskite top cell. However, careful understanding of the optical and electrical properties of each functional layer is expected to be the core process to further promote efficiency. Regarding the environmental and intrinsic instability issues, encapsulation is considered to be the most effective method to address environmental instability. Preventing ion migration is one of the fundamental methods to eliminate intrinsic instability. It is believed that low dimensional perovskite materials will become a competitive solution to simultaneously solve these two instabilities. Finally, some suggestions for reducing costs and preparation of PK/c-Si tandem on a large-scale are also discussed which provides guidance for further boosting the development of PK/c-Si tandem.

Non-fullerene acceptors used in organic solar cells often crystallize when they are solution processsed. ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit various polymorphs, including a metastable form that is readily promoted via solution processing and leads to the highest device efficiencies despite exhibiting poor order along the π–π stacking direction.

Abstract

Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.

In article number 2100316, Xiao-Tao Hao and co-workers investigate the stabilizing function of alloy states from the perspective of controlling the aggregation of non-fullerene acceptors. The acceptor alloys strengthen the conformational rigidity of BTP-4Cl to restrain the intramolecular vibrations for rapid relaxation of high-energy excited states to stabilize BTP-4Cl. The donor alloys optimize the fibril network microstructure of PM6 to restrict the aggregation of BTP-4Cl.

A super stretchable electroluminescent device is successfully fabricated with double-network ionogel as a soft electrode owing to its excellent mechanical robustness and electrical conductivity. The fabricated device exhibits extremely stable light-emitting operation even at high elongation as well as demonstrating mechanical, electrical, and thermal stability, which can be applied to new types of stretchable light display and sensors.

Abstract

Ionogels are good candidates for flexible electronics owing to their excellent mechanical and electrical properties, including stretchability, high conductivity, and stability. In this study, conducting ionogels comprising a double network (DN) of poly(N-isopropylacrylamide-co-N,N′-diethylacrylamide)/chitosan which are further reinforced by the ionic and covalent crosslinking of the chitosan network by tripolyphosphate and glutaraldehyde, respectively, are prepared. Based on their excellent mechanical properties and high conductivity, the developed DN ionogels are envisioned as stretchable ionic conductors for extremely stretchable alternating-current electroluminescent (ACEL) devices. The ACEL device fabricated with the developed ionogel exhibits stable working operation under an ultrahigh elongation of over 1200% as well as severe mechanical deformations such as bending, rolling, and twisting. Furthermore, the developed ACEL devices also display stable luminescence over 1000 stretch/release cycles or at temperatures as harsh as 200 °C.

Fully 3D printed and disposable paper supercapacitors are designed from the bottom up by a combination of nanocellulose, biopolymers, and carbon nanomaterials leading to monolithic integrated devices with excellent electrochemical properties. The results combining digital material assembly, high performance, and nontoxicity have the potential to move the field of sustainable electronics forward.

Abstract

With the development of the internet-of-things for applications such as wearables and packaging, a new class of electronics is emerging, characterized by the sheer number of forecast units and their short service-life. Projected to reach 27 billion units in 2021, connected devices are generating an exponentially increasing amount of electronic waste (e-waste). Fueled by the growing e-waste problem, the field of sustainable electronics is attracting significant interest. Today, standard energy-storage technologies such as lithium-ion or alkaline batteries still power most of smart devices. While they provide good performance, the nonrenewable and toxic materials require dedicated collection and recycling processes. Moreover, their standardized form factor and performance specifications limit the designs of smart devices. Here, exclusively disposable materials are used to fully print nontoxic supercapacitors maintaining a high capacitance of 25.6 F g⁻¹ active material at an operating voltage up to 1.2 V. The presented combination of digital material assembly, stable high-performance operation, and nontoxicity has the potential to open new avenues within sustainable electronics and applications such as environmental sensing, e-textiles, and healthcare.