lizhendong

The process of accurately gauging lifetime improvements in organic photovoltaics (OPVs) or other similar emerging technologies, such as perovskites solar cells is still a major challenge. The presented work is part of a larger effort of developing a worldwide database of lifetimes that can help establishing reference baselines of stability performance for OPVs and other emerging PV technologies, which can then be utilized for pass-fail testing standards and predicting tools. The study constitutes scanning of literature articles related to stability data of OPVs, reported until mid-2015 and collecting the reported data into a database. A generic lifetime marker is utilized for rating the stability of various reported devices. The collected data is combined with an earlier developed and reported database, which was based on articles reported until mid-2013. The extended database is utilized for establishing the baselines of lifetime for OPVs tested under different conditions. The work also provides the recent progress in stability of unencapsulated OPVs with different architectures, as well as presents the updated diagram of the reported record lifetimes of OPVs. The presented work is another step forward towards the development of pass-fail testing standards and lifetime prediction tools for emerging PV technologies.

An extended database of lifetime for organic photovoltaics is presented. The data is utilized for establishing lifetime baselines for the samples tested under different aging conditions. The baselines can serve as a reference for gauging the improvements in device lifetimes in future reports. Encapsulated and unencapsulated samples with the best lifetimes reported in literature so far are listed as well.

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.

In this work, the detailed morphology studies of polymer poly(3-hexylthiophene-2,5-diyl) (P3HT):fullerene(PCBM) and polymer(P3HT):polymer naphthalene diimide thiophene (PNDIT) solar cell are presented to understand the challenge for getting high performance all-polymer solar cells. The in situ X-ray scattering and optical interferometry and ex situ hard and soft X-ray scattering and imaging techniques are used to characterize the bulk heterojunction (BHJ) ink during drying and in dried state. The crystallization of P3HT polymers in P3HT:PCBM bulk heterojunction shows very different behavior compared to that of P3HT:PNDIT BHJ due to different mobilities of P3HT in the donor:acceptor glass. Supplemented by the ex situ grazing incidence X-ray diffraction and soft X-ray scattering, PNDIT has a lower tendency to form a mixed phase with P3HT than PCBM, which may be the key to inhibit the donor polymer crystallization process, thus creating preferred small phase separation between the donor and acceptor polymer.

The morphology development of polymer:fullerene and polymer:polymer solar cells is characterized by real-time X-ray scattering and interferometry. Polymer:fullerence blends show a smaller phase-separation due to high glass-transition temperature of PCBM acceptors, compared to polymer:polymer blends.

Hybrid organic–inorganic halide perovskites have emerged at the forefront of solution-processable photovoltaic devices. Being the perovskite precursor mixture a complex equilibrium of species, it is very difficult to predict/control their interactions with different substrates, thus the final film properties and device performances. Here the wettability of CH₃NH₃PbI₃ (MAPbI₃) onto poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer is improved by exploiting the cooperative effect of graphene oxide (GO) and glucose inclusion. The glucose, in addition, triggers the reduction of GO, enhancing the conductivity of the PEDOT:PSS+GO+glucose based nanocomposite. The relevance of this approach toward photovoltaic applications is demonstrated by fabricating a hysteresis-free MAPbI₃ solar cells displaying a ≈37% improvement in power conversion efficiency if compared to a device grown onto pristine PEDOT:PSS. Most importantly, V_OC reaches values over 1.05 V that are among the highest ever reported for PEDOT:PSS p-i-n device architecture, suggesting minimal recombination losses, high hole-selectivity, and reduced trap density at the PEDOT:PSS along with optimized MAPbI₃ coverage.

The synergistic effect of graphene oxide and glucose in improving the conduction properties of polymer electrolyte poly(3,4-ethyl­enedioxythiophene):poly­(styrenesul­fonate) and modifying the sensible interface of perovskite solar cells is reported. This method allows obtaining hysteresis-free and high V_OC CH₃NH₃PbI₃ devices displaying a ≈37% improvement in power conversion efficiency, evidencing minimal recombination losses and very efficient charge extraction at the electrodes.

Well-defined small molecule (SM) donors can be used as alternatives to π-conjugated polymers in bulk-heterojunction (BHJ) solar cells with fullerene acceptors (e.g., PC₆₁/₇₁BM). Taking advantage of their synthetic tunability, combinations of various donor and acceptor motifs can lead to a wide range of optical, electronic, and self-assembling properties that, in turn, may impact material performance in BHJ solar cells. In this report, it is shown that changing the sequence of donor and acceptor units along the π-extended backbone of benzo[1,2-b:4,5-b′]dithiophene–6,7-difluoroquinoxaline SM donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin-films, and (iii) charge transport in BHJ solar cells. In these systems (SM1-3), it is found that 6,7-difluoroquinoxaline ([2F]Q) motifs directly appended to the central benzo[1,2-b:4,5-b′]dithiophene (BDT) unit yield a lower-bandgap analogue (SM1) with favorable molecular packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%. ¹H-¹H DQ-SQ NMR analyses indicate that SM1 and its counterpart with [2F]Q motifs substituted as end-group SM3 possess distinct self-assembly patterns, correlating with the significant charge transport and BHJ device efficiency differences observed for the two analogous SM donors (avg. 6.3% vs 2.0%, respectively).

Changing the sequence of donor and acceptor units along the π-extended backbone of benzo[1,2-b:4,5-b′]dithiophene–6,7-difluoroquinoxaline small molecule (SM) donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin-films, and (iii) charge transport in bulk-heterojunction (BHJ) solar cells. The lower-bandgap analogue (SM1) achieves distinct local packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%.

A low-bandgap (1.33 eV) Sn-based MA_0.5FA_0.5Pb_0.75Sn_0.25I₃ perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI₃ cell to achieve a high efficiency of 19.08%.

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%.

Visualizing behaviors of cell populations within living multicellular organisms in real time is of great value to life science but challenging due to the lack of ideal probes. In this work, a biocompatible fluorogen, azide-functionalized tetraphenylethene pyridinium (TPE-PyN₃), is reported for noninvasive imaging and sensing within living systems. TPE-PyN₃ exhibits unique aggregation-induced emission (AIE) attributes and high affinity to mitochondria, enabling it to achieve specific mitochondrial imaging and long-term cellular observing with excellent photostability both in vitro and in vivo. The high membrane penetrability of TPE-PyN₃ allows all of the cells within the living zebrafish embryos to be morphologically visualized and reconstructed in 3D. Moreover, TPE-PyN₃ is capable of indicating cell apoptosis because of its sensitivity to the change of mitochondrial membrane potential. The findings presented here provide a simple and noninvasive tool for studying behaviors of cell populations in vivo for the first time by a small-molecule AIE probe.

An aggregation-induced emission active probe with distinctive properties for biological imaging and sensing in cultured cells and in living systems is presented. Novel applications of this probe such as in situ cellular imaging and cell apoptosis detection in living zebrafish embyros are demonstrated.

A new type of organic light-emitting diode (OLED) has emerged that shows enhanced operational stability and large internal quantum efficiency approaching 100%, which is based on thermally activated delayed fluorescence (TADF) compounds doped with fluorescent emitters. Magneto-electroluminescence (MEL) in such TADF-based OLEDs and magneto-photoluminescence (MPL) in thin films based on donor–acceptor (D–A) exciplexes doped with fluorescent emitters with various concentrations are investigated. It has been found that both MEL and MPL responses are thermally activated with substantially lower activation energy compared to that in the pristine undoped D–A exciplex host blend. In addition, both MPL and MEL steeply decrease with the emitter's concentration. This indicates the existence of a loss mechanism, whereby the triplet charge-transfer state in the exciplex host blend may directly decay to the lowest, nonemissive triplet state of the fluorescent emitter molecules.

Using magneto-electroluminesence in organic light-emitting diodes of donor–acceptor exciplex compounds doped with fluorescence emitters, we found that the activation energy of the reversed intersystem crossing process is substantially reduced compared with that of the undoped compound. At lower dopant concentration, the rapid Förster energy transfer enhances the electro-luminesence, whereas at higher dopant concentration Dexter energy transfer interferes, creating a loss mechanism.

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.

Highly bright light-emitting diodes based on solution-processed all-inorganic perovskite thin film are demonstrated. The cesium lead bromide (CsPbBr₃) created using a new poly(ethylene oxide)-additive spin-coating method exhibits photoluminescence quantum yield up to 60% and excellent uniformity of electrical current distribution. Using the smooth CsPbBr₃ films as emitting layers, green perovskite-based light-emitting diodes (PeLEDs) exhibit electroluminescent brightness and efficiency above 53 000 cd m⁻² and 4%: a new benchmark of device performance for all-inorganic PeLEDs.

Electron-filtering compound buffer layers (EF-CBLs) improve charge extraction in organic photovoltaic cells (OPVs) by blending an electron-conducting fullerene with a wide energy gap exciton-blocking molecule. It is found that devices with EF-CBLs with high glass transition temperatures and a low crystallization rate produce highly stable morphologies and devices. The most stable OPVs employ 1:1 2,2′,2″-(1,3,5-benzenetriyl tris-[1-phenyl-1H-benzimidazole] TPBi:C₇₀ buffers that lose <20% of their initial power conversion efficiency of 6.6 ± 0.6% after 2700 h under continuous simulated AM1.5G illumination, and show no significant degradation after 100 days of outdoor aging. When exposed to 100-sun (100 kW m⁻²) concentrated solar illumination for 5 h, their power conversion efficiencies decrease by <8%. Moreover, it is found that the reliability of the devices employing stable EF-CBLs has either reduced or no dependence on operating temperature up to 130 °C compared with BPhen:C₆₀ devices whose fill factors show thermally activated degradation. The robustness of TPBi:C₇₀ devices under extreme aging conditions including outdoor exposure, high temperature, and concentrated illumination is promising for the future of OPV as a stable solar cell technology.

The operational lifetime of planar-mixed heterojunction small molecule organic photovoltaic cells is dramatically improved by employing a morphologically stable electron-filtering compound cathode buffer layer. The devices can withstand extreme environmental stress, including > 2500 hr under 1 sun at 130 ºC, many hours of 100 sun illumination and months of outdoor exposure while maintaining >80% of their starting efficiency.

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.

Controlling the morphology and surface passivation in perovskite solar cells is paramount in obtaining optimal optoelectronic properties. This study incorporates N-doped graphene nanosheets in the perovskite layer, which simultaneously induces an improved morphology and surface passivation at the perovskite/spiro interface, resulting in enhancement in all photovoltaic parameters.

An organic–inorganic halide CH₃NH₃SnI₃ perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. The mechanism underlying the enhanced properties is shown to be associated with the pressure-induced structural modification.

The performance of hybrid perovskite-based light-emitting diodes (LEDs) is markedly enhanced by the application of a NiO_x electrode interlayer and moderate methylamine treatment. A hybrid perovskite-based LED exhibits a peak luminous efficiency of 15.9 cd A⁻¹ biased at 8.5 V, 407.65 mA cm⁻², and 65 300 cd m⁻², showing a distinctive impact for future applications.