wangzhaowei

A method to prepare aqueous metal oxide inks for tuning the work function (WF) of electrodes is demonstrated. Thin films prepared from the metal oxide ink based on vanadium oxide (V₂O₅) nanoparticles are found to increase the WF of an indium-tin-oxide (ITO) electrode. ITO substrates modified with V₂O₅ films are applied as a hole selective layer (HSL) in polymer solar cells (PSCs) using a poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester blend as a photoactive layer. The PSCs prepared with V₂O₅-modified ITO show better device performance, achieving a power conversion efficiency of 3.6%, demonstrating 15% enhancement compared to conventional ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT-PSS) based devices. Furthermore, ITO/V₂O₅-modified devices exhibit better ambient stability with 60% improvement in device lifetime than those using PEDOT:PSS as an HSL. This solution-processable and highly stable WF-modifying metal oxide film can be a potential alternative material for engineering interfaces in optoelectronic devices.

The electrode work function is modified using a facile method. Aqueous inks of high work function metal oxides are developed for use as solution-processable hole extraction layers in polymer solar cells. Devices incorporating the newly developed inks present excellent device efficiency and stability, and have potential to be an alternative high work function material to poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate).

Metal nanoparticles are demonstrated to boost the internal quantum efficiency (IQE) of organic solar cells (OSCs), even without a notable plasmonic optical gain. A hybrid layer platform in combination with silver nanoparticles (AgNPs) and a polyethylenimine-ethoxylated (PEIE) layer maximize the IQE of the OSCs to nearly 100%, yielding a power conversion efficiency (PCE) of 10.1% in the OSCs. 2D surface characterization confirmed that the AgNPs provide a short path and funneled charge carriers to the cathode, thus effectively increasing the carrier mobility. Moreover, the hybrid layer doubles the device's half-efficiency lifetime due to the longer retention of the improved mobility.

Metal nanoparticles (NPs) improve the performance of organic solar cells by enhancing the internal quantum efficiency (IQE) and stability of the devices. An IQE level of approximately 100% is achieved by embedding the AgNPs in an electron-transporting layer in organic solar cells with an inverted structure. The AgNPs in the polyethylenimine-ethoxylated (PEIE) layer facilitates charge carrier generation and transport and improves the stability of the organic solar cells.

Highly efficient solar cells with sustainable performance under severe mechanical deformations are in great demand for future wearable power supply devices. In this regard, numerous studies have progressed to implement flexible architecture to high-performance devices such as perovskite solar cells. However, the absence of suitable flexible and stretchable materials has been a great obstacle in the replacement of largely utilized transparent conducting oxides that are limited in flexibility. Here, a shape recoverable polymer, Noland Optical Adhesive 63, is utilized as a substrate of perovskite solar cell to enable complete shape recovery of the device upon sub-millimeter bending radii. The employment of stretchable electrodes prevents mechanical damage of the perovskite layer. Before and after bending at a radius of 1 mm, power conversion efficiency (PCE) is measured to be 10.75% and 10.4%, respectively. Additionally, the shape recoverable device demonstrates a PCE of 6.07% after crumpling. The mechanical properties of all the layers are characterized by nanoindentation. Finite element analysis reveals that the outstanding flexibility of the perovskite layer enables small plastic strain distribution on the deformed device. These results clearly demonstrated that this device has great potential to be utilized in stretchable power supply applications.

Indium tin oxide-free and shape-recoverable perovskite solar cells with a high-power conversion efficiency (PCE = 10.83%) and an excellent mechanical durability (PCE = 9.68% after 1000 bending cycle at r = 1 mm bending radius) is demonstrated. The mechanical behavior of intrinsically flexible and stretchable perovskite layer is thoroughly investigated by nanoindentation measurements and finite element analysis.

A novel D-A₁-D-A₂-type polymer that exhibits a small bandgap of 1.43 eV yet still yields polymer solar cells with a high open-circuit voltage (V_OC) of 0.81 V and power conversion efficiencies of up to 8.63% is reported. Comparable efficiencies can be achieved even when the active layer is processed in air or after it is thermally annealed at 150 °C.

The photovoltaic performance of perovskite solar cells (PVSCs) is extremely dependent on the morphology and crystallization of the perovskite film, which is affected by the deposition method. In this work, a new approach is demonstrated for forming the PbI₂ nanostructure and the use of high CH₃NH₃I concentration which are adopted to form high-quality (smooth and PbI₂ residue-free) perovskite film with better photovoltaic performances. On the one hand, self-assembled porous PbI₂ is formed by incorporating small amount of rationally chosen additives into the PbI₂ precursor solutions, which significantly facilitate the conversion of perovskite without any PbI₂ residue. On the other hand, by employing a relatively high CH₃NH₃I concentration, a firmly crystallized and uniform CH₃NH₃PbI₃ film is formed. As a result, a promising power conversion efficiency of 16.21% is achieved in planar-heterojunction PVSCs. Furthermore, it is experimentally demonstrated that the PbI₂ residue in perovskite film has a negative effect on the long-term stability of devices.

A new approach for forming the PbI₂ nanostructure and high CH₃NH₃I concentration are used to form high-quality, smooth, and PbI₂ residue-free, perovskite films with better photovoltaic performance. PbI₂ residue in perovskite films is demonstrated to have a negative effect on the long-term stability of perovskite solar cells.

In recent years, there has been an unprecedented rise in the performance of metal halide perovskite solar cells. They are now in a position to compete on performance with traditional crystalline solar cells, and as such the most pressing questions concern the long term operational stability of this class of solar cell. Here, recent developments in understanding and overcoming stability concerns of metal halide perovskite solar cells are highlighted. An overview of possible instability issues due to electrical, atmospheric, heat, and light stresses is provided and the different implications to the most commonly used device architectures are discussed.

Metal halide perovskite solar cells are in a position to compete on performance with traditional crystalline solar cells and, as such, the most pressing questions concern the long term operational stability of this class of solar cells. Recent developments in understanding and overcoming stability concerns of metal halide perovskite solar cells are highlighted.

In situ control of perovskite absorber properties enables a record-efficiency two-terminal monolithic perovskite-CIGS tandem thin-film solar cell.

Establishing renewable energy sources is currently one of the major scientific topics. Two aspects are most crucial: energy conversion and energy storage. Thus, the development of efficient solar-cell devices and high-capacity, high-current rechargeable battery systems turns out to be of great importance. In particular, the design of active materials and their characterization using electrochemical and spectroscopic means represent essential elements in the development process. Here, a concise overview of both methods and key properties with regard to the characterization of organic and polymeric active materials with a focus on energy conversion/storage is provided. Benefits and limitations of complementary techniques are presented to enable a consistent and comprehensive characterization procedure.

With regard to a changing worldwide energy distribution policy towards renewable systems, more and more research is focused on solar-based energy conversion and related energy-storage technologies. Basic techniques for the characterization and development of solar cells and battery devices that are based on organic and polymeric active materials are discussed.

Organic ternary heterojunction photovoltaic blends are sometimes observed to undergo a gradual evolution in open-circuit voltage (V_oc) with increasing amounts of a second donor or an acceptor. The V_oc is strongly correlated with the energy of the charge transfer state in the blend, but this value depends on both local and mesoscopic orders. In this work, the behavior of V_oc in the presence of a wide range of interfacial electronic states is investigated. The key charge transfer state interfaces responsible for V_oc in several model systems with varying morphology are identified. Systems consisting of one donor with two fullerene molecules and of one acceptor with a donor polymer of varying regio-regularity are used. The effects from the changing energetic disorder in the material and from the variation due to a law of simple mixtures are quantified. It has been found that populating the higher-energy charge transfer states is not responsible for the observed change in V_oc upon the addition of a third component. Aggregating polymers and miscible fullerenes are compared, and it has been concluded that in both cases charge delocalization, aggregation, and local polarization effects shift the lowest-energy charge transfer state distribution.

The open-circuit voltage evolution and charge transfer state interfaces in ternary organic photovoltaic blends are investigated using several model systems. The changes in subgap spectra from energetic disorder and increased population of higher energy states are analyzed and the lowest charge transfer state distribution is observed to shift due to local aggregation and delocalization effects.

For lead halide perovskite solar cells to be considered for large-scale commercial applications, the active material must be proven to be fundamentally stable under relevant operating conditions, such as exposure to light, heat, ambient environment, and electrical bias. Reversible and irreversible effects upon applying an electric field under different environmental conditions are identified. The application of an electric field in inert conditions leads only to a reversible poling on a time scale of minutes, whose distribution is mapped throughout the semiconductor film. It is also found that the presence of moisture, and in general of small polar and hydrogen-bonding molecules, results in an irreversible degradation in the presence of the electric field, which happens in a time scale of hours under conditions relevant for photovoltaic operation. The measurements here suggest that the irreversible field-induced degradation in air occurs via a hydrated phase, in which the organic cation is loosely bound and can drift in response to an electric field, finally degrading the material to PbI₂. This has direct relevance to perovskite solar cells; hysteretic behavior in current–voltage curves is aggravated by the presence of moisture while devices aged under load accelerates degradation.

Ion motion and associated degradation pathways in methylammonium trihalide perovskites are investigated in dry and humid conditions. A combination of optical, electrical, structural, and elemental mapping of lateral devices shows that ion migration in inert conditions is primarily reversible and occurs through defect motion, while under humid conditions significant methylammonium ion drift results in irreversible structural degradation.

The improved performance achieved by combining tert-butyl copper (II) phthalocyanine (CuPC) and po-spiro-OMeTAD as hole transporting material (HTM) for formamidinium lead iodide (FAPbI₃)-based perovskite solar cells is reported. A device efficiency of 19.4% under standard 1 sun is obtained.

The effect of substituting lead with tin in perovskite-based solar cells (PSCs) has shows that lead is preferred over tin by a lower cumulative energy demand. The results, which also include end-of-life management, show that a recycling scenario that carefully handles emission of lead enables use of lead in PSCs with little environmental impact. All other scenarios result in catastrophic emission of lead to the environment that would spell an end to widespread use of lead in PSCs.

With the aim of fully utilizing the low processing temperatures of perovskite solar cells, significant progress in replacing high temperature processed TiO₂ by various low-temperature solution processed electron transporting layers (LT-ETLs) was recently reported. Here, recent progress in the development of LT-ETLs for regular planar structure perovskite solar cells, which is essential for achieving high efficiency in parallel to avoiding hysteresis, is reviewed. In addition, the application of a novel hysteresis-free LT-ETLs for regular planar perovskite solar cells in our laboratory is briefly discussed. By incorporating a low temperature processed WO_x nanoparticular layer in combination with a mixed fullerene functionalized self-assembled monolayers (SAMs), a regular, planar structure, and hysteresis-free perovskite solar cell with a maximum efficiency of almost 15% can be fabricated.

Recent progress in the development of low temperature processed electron-transporting layers for regular planar structure perovskite solar cells is reviewed. Moreover, the application of a novel mixed self-assembled monolayers in hysteresis-free perovskite solar cells is briefly discussed. The as-fabricated perovskite solar cells show a maximum efficiency of almost 15%.

Polymers based on thieno[3,4-c]pyrrole-4,6-dione derivatives are interesting and promising candidates for organic bulk heterojunction solar cells. Herein, a series of push–pull conjugated polymers based on thieno[3,4-c]pyrrole-4,6-dione (TPD), furo[3,4-c]pyrrole-4,6-dione (FPD), and selenopheno[3,4-c]-pyrrole-4,6-dione (SePD) have been synthesized by direct heteroarylation polymerization and fully characterized. The impacts of both the heteroatom (sulfur, oxygen, and selenium) and the side chain (branched or linear) of [3,4-c]pyrrole-4,6-dione unit on the electro-optical properties have been investigated. Among polymers developed, two new highly processable terthiophene–SePD (P4) and dithienosilole–SePD (P9) copolymers led to air-processed polymer solar cells with power conversion efficiencies of 5.1% and 7.1% using the following inverted configuration: ITO/ZnO/Polymer:PCBM/MoO₃/Ag. These promising results make P4 and P9 good candidates for further upscaling and device optimization.

A series of conjugated polymers based on thieno, furo, and selenopheno[3,4-c]-pyrrole-4,6-dione (TPD, FPD, SePD) have been synthesized and fully characterized. The impacts of both the heteroatom and the side chain of [3,4-c]pyrrole-4,6-dione unit on the electro-optical properties have been investigated. Two new materials based on SePD led to air-processed polymer solar cells with power conversion efficiency up to 7.1%.

Au@SiO₂@Ag@SiO₂ core–triple shell nanoparticles are fabricated by a wet-chemical approach and characterized. Each SiO₂ layer is given a special function, which enhances the surface plasmon resonance to improve light harvesting and reduce interfacial carrier recombination in dye-sensitized solar cells. The photo-anode with Au@SiO₂@Ag@SiO₂ obtains an energy conversion efficiency of up to 9.22%.

Although power conversion efficiency (PCE) of state-of-the-art perovskite solar cells has already exceeded 20%, photo- and/or moisture instability of organolead halide perovskite have prevented further commercialization. In particular, the underlying weak interaction of organic cations with surrounding iodides due to eight equivalent orientations of the organic cation along the body diagonals in unit cell and chemically non-inertness of organic cation result in photo- and moisture instability of organometal halide perovskite. Here, a perovskite light absorber incorporating organic–inorganic hybrid cation in the A-site of 3D APbI₃ structure with enhanced photo- and moisture stability is reported. A partial substitution of Cs⁺ for HC(NH₂)₂⁺ in HC(NH₂)₂PbI₃ perovskite is found to substantially improve photo- and moisture stability along with photovoltaic performance. When 10% of HC(NH₂)₂⁺ is replaced by Cs⁺, photo- and moisture stability of perovskite film are significantly improved, which is attributed to the enhanced interaction between HC(NH₂)₂⁺ and iodide due to contraction of cubo-octahedral volume. Moreover, trap density is reduced by one order of magnitude upon incorporation of Cs⁺, which is responsible for the increased open-circuit voltage and fill factor, eventually leading to enhancement of average PCE from 14.9% to 16.5%.

FA_0.9Cs_0.1PbI₃ with improved moisture- and photostability is developed. Incorporation of 10% of Cs cation in the FA cation sites improves photovoltaic performance as well as photo- and moisture stability. Property–structure correlation plays important role in improving the stability of perovskite solar cells.