wangzhaowei

Recently, the rapid and significant progress in the development of various stretchable electronics has triggered intense research interest. Although the remarkable features of transfer printing processes have enabled the use of inorganic crystalline semiconductors in various types of stretchable devices, including solar cells, light-emitting diodes, circuits, and photodetectors, there are few examples of stretchable electronics using thin film semiconductors. Transfer printing of inorganic amorphous thin film semiconductors remains a challenge because no suitable sacrificial layer is available. To meet this challenge, a water-soluble germanium oxide sacrificial layer is developed. Stretchable inorganic amorphous thin film solar cells are produced using a transfer printing process with a water-soluble sacrificial layer. This first attempt to fabricate stretchable solar cells with inorganic amorphous thin film semiconductors significantly broadens the scope of solar cell applications. Moreover, the germanium oxide sacrificial layer can be used in other thin film electronics applications.

Water-soluble germanium oxide sacrificial layer for transfer printing of thin film solar cells is developed. The main advantages of a germanium oxide sacrificial layer are no use of corrosive reagents in the etching process, compatibility with high-temperature processes. Stretchable thin film solar cells are produced for the first time using this transfer printing process with a water-soluble sacrificial layer.

The radiation hardness of CH₃NH₃PbI₃-based solar cells is evaluated from in situ measurements during high-energy proton irradiation. These organic–inorganic perovskites exhibit radiation hardness and withstand proton doses that exceed the damage threshold of crystalline silicon by almost 3 orders of magnitude. Moreover, after termination of the proton irradiation, a self-healing process of the solar cells commences.

A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX₃, X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.

Spray-coating is a versatile coating technique that can be used to deposit functional films over large areas at speed. Here, spray-coating is used to fabricate inverted perovskite solar cell devices in which all of the solution-processible layers (PEDOT:PSS, perovskite, and PCBM) are deposited by ultrasonic spray-casting in air. Using such techniques, all-spray-cast devices having a champion power conversion efficiency (PCE) of 9.9% are fabricated. Such performance compares favorably with reference devices spin-cast under a nitrogen atmosphere that has a champion PCE of 12.8%. Losses in device efficiency are ascribed to lower surface coverage and reduced uniformity of the spray-cast perovskite layer.

Spray-coating is a versatile coating technique that can be used to deposit functional films over large areas at speed. Here, the authors fabricate inverted perovskite solar cell devices in which all of the solution-processible layers are deposited by ultrasonic spray-casting in air leading to all-spray-cast devices having a champion power conversion efficiency of 9.9%.

Metal halide perovskites have emerged as one of the most promising materials for photovoltaics (PVs), with power conversion efficiency of over 22% already demonstrated. In order to compete with traditional crystalline silicon PV, cost and stability are equally important issues that need to be considered besides efficiency. Copper thiocyanate (CuSCN) is an interesting candidate to be used as an inexpensive, thermally stable p-type charge conducting material in perovskite solar cells. Here, we report 13% efficient perovskite solar cells employing CuSCN as the hole-transport material. We compare the stability of cells employing CuSCN with those employing the archetypical organic hole-transporter 2,2′,7,7′-Tetrakis (N,N-di-p-methoxyphenyl-amine) 9,9′-Spirobifluorene (Spiro-OMeTAD), under elevated temperature in ambient atmosphere. Surprisingly, we find that the devices employing CuSCN degrade faster under elevated temperatures than the devices employing Spiro-OMeTAD. We discover that an interfacial degradation mechanism occurs at the heterojunction between the perovskite absorber and the CuSCN, even in a dry nitrogen atmosphere, identifying the presence of a critical instability. Interestingly, with the additional coating of the completed cells with a thin film of insulating poly(methyl methacrylate) (PMMA), functioning as a rudimentary “on-cell” encapsulation, we significantly alleviate this issue and deliver efficient perovskite solar cells which survive for more than 1000 hours at 85 °C in air with only 25% degradation in performance. Beyond identifying a critical area to address in order to enable CuSCN to be useful for long term operation in perovskite solar cells, our findings indicate that the role of the “encapsulant” is to both keep the environment out, and keep degradation products within the cell.

An interfacial degradation mechanism occurring at the heterojunction between the perovskite absorber and the CuSCN is discovered, identifying the presence of a critical instability. This issue can be alleviated with the additional coating of the completed cells with a thin film of insulating layer, delivering efficient perovskite solar cells with outstanding thermal stability.

In this study, it is demonstrated that a facile room-temperature processed amine functionalized perylene-diimide (PDIN) can function as an efficient electron-transporting layer (ETL) to enhance the photovoltaic performance of inverted PDI-based non-fullerene solar cells. It is showed that the PDIN ETL possesses respectable mobilities and interfacial doping capability to the PDI-based acceptors to facilitate the charge transport and extraction in the devices. Moreover, it can modulate the morphological evolution of the bulk-heterojunction (BHJ) atop to result in a more crystalline, face-on orientation because of its improved compatibility to PDI-based acceptors. Consequently, the PDIN ETL enables the derived devices to have 10% higher power conversion efficiency (PCE) than the reference device. In addition, the PDIN can also be used as a surface modifier on ZnO to result in a ≈14% enhanced PCE than that of the pristine ZnO-based device. This study shows the feasibility of modulating the BHJ of non-fullerene organic photovoltaics by rationally selected ETLs to facilitate exciton dissociation and collection of the devices.

A room-temperature processable organic perylene-diimide-based electron-transporting layer (ETL) is demonstrated to enhance the performance of inverted PDI-based organic solar cells. The amine functionalized perylene-diimide ETL can effectively modulate bulk-heterojunction morphology atop to induce improved out-of-plane π–π stacking and associated lamellar orientation. Consequently, it can replace or modify the regularly used ZnO ETL for enhanced photovoltaic performance.

Ionic liquids can retard the perovskite crystallization with the aim to form compact films with larger and more uniformly distributed grain size. The ionic liquid driven crystallization is exploited to prepared a record planar perovskite solar cell with stabilized power output of 19.5%.

A crosslinked organic hole-transporting layer (HTL) is developed to realize highly efficient and stable perovskite solar cells via a facile thiol-ene thermal reaction. This crosslinked HTL not only facilitates hole extraction from perovskites, but also functions as an effective protective barrier. A high-performance (power conversion efficiency: 18.3%) device is demonstrated to show respectable photo and thermal stability without encapsulation.

Molecular orientation plays a critical role in determing the performance of all-polymer solar cells. In article number 1600504, Bumjoon J. Kim and co-workers report an approach for tuning the molecular crystallinity and orientation of naphthalenediimide-bithiophene-based n-type polymers (P(NDI2HD-T2)) by controlling their number average molecular weights. The cover image depicts the bulk heterojunction all-polymer solar cell with PTB7-Th donor and P(NDI2HD-T2) acceptor. The packing orientation of two polymers in thin film and at the interface is critical for producing high-performance solar cells.

Morphology plays a vital role on the performance of organic photovoltaics. However, our understanding of the morphology-performance relationships for organic photovoltaics remains lacking. Specifically, it is still an open question why some bulk-heterojunction blends exhibit electric field dependent J–V curves, while others do not. Through detailed fs-μs transient absorption spectroscopy and morphology studies on the representative bulk-heterojunction type small molecule (SM) donor system, a picture of different J–V behaviors from morphology aspects and excited dynamics is revealed. Our findings reveal that amorphous morphology in the lack of percolated pathways leads to the formation of strongly bound charge transfer states (CTSs), which accounts for about one third of the photoexcited species. Therefore, field-dependent J–V curves are obtained as these CTSs mainly undergo geminate recombination or function as interfacial traps for nongeminate recombination. On the other hand, the CTSs are totally suppressed after post-treatment owning to the formation of bicontinuous morphology, which results in very high efficiencies from exciton generation, diffusion, dissociation to charge extraction, thus contributes to field-independent J–V characteristics. The insights gained in this work provide the effective guidelines to further optimize the performance of bulk-heterojunction type SM-organic photovoltaics through judicious morphology control and engineering.

A picture of different J–V behaviors from morphology aspects and excited dynamics is revealed through fs-μs transient absorption measurements. The amorphous donor morphology without percolated pathways facilitates the formation of strongly bound charge transfer states, which results in the field-dependent J–V curves as these charge transfer states can only be dissociated and extracted by applying very large reverse voltages.

The incorporation of multiple donors into the bulk-heterojunction layer of organic polymer solar cells (PSCs) has been demonstrated as a practical and elegant strategy to improve photovoltaics performance. However, it is challenging to successfully design and blend multiple donors, while minimizing unfavorable interactions (e.g., morphological traps, recombination centers, etc.). Here, a new Förster resonance energy transfer-based design is shown utilizing the synergistic nature of three light active donors (two small molecules and a high-performance donor–acceptor polymer) with a fullerene acceptor to create highly efficient quaternary PSCs with power conversion efficiencies (PCEs) of up to 10.7%. Within this quaternary architecture, it is revealed that the addition of small molecules in low concentrations broadens the absorption bandwidth, induces cocrystalline molecular conformations, and promotes rapid (picosecond) energy transfer processes. These results provide guidance for the design of multiple-donor systems using simple processing techniques to realize single-junction PSC designs with unprecedented PCEs.

A viable strategy to realize highly efficient quaternary blend solar cells is introduced that breaks efficiency above 10% with complementary squaraine small molecules–low band-gap polymer combinations. Our quaternary design demonstrates several advantages: (i) broader light absorption, (ii) improved surface morphology, (iii) enhanced cocrystallization packing, (iv) multiple energy and charge transfer pathways to reduce recombination, and (v) increased charge mobility.