Abstract
The benchmark tin oxide (SnO
2
) electron transporting layers (ETLs) have enabled remarkable progress in planar perovskite solar cell (PSCs). However, the energy loss is still a challenge ...due to the lack of “hidden interface” control. We report a novel ligand-tailored ultrafine SnO
2
quantum dots (QDs)
via
a facile rapid room temperature synthesis. Importantly, the ligand-tailored SnO
2
QDs ETL with multi-functional terminal groups in situ refines the buried interfaces with both the perovskite and transparent electrode
via
enhanced interface binding and perovskite passivation. These novel ETLs induce synergistic effects of physical and chemical interfacial modulation and preferred perovskite crystallization-directing, delivering reduced interface defects, suppressed non-radiative recombination and elongated charge carrier lifetime. Power conversion efficiency (PCE) of 23.02% (0.04 cm
2
) and 21.6% (0.98 cm
2
,
V
OC
loss: 0.336 V) have been achieved for the blade-coated PSCs (1.54 eV
E
g
) with our new ETLs, representing a record for SnO
2
based blade-coated PSCs. Moreover, a substantially enhanced PCE (
V
OC
) from 20.4% (1.15 V) to 22.8% (1.24 V, 90 mV higher
V
OC
, 0.04 cm
2
device) in the blade-coated 1.61 eV PSCs system, via replacing the benchmark commercial colloidal SnO
2
with our new ETLs.
Effects of water and oxygen exposures on electronic structures of the bathocuproine (BCP)/fullerene (C60) interface were studied by photoemission spectroscopies. C60 in BCP/C60 interface prepared ...under ultrahigh vacuum (UHV) shows a downward energy level bending of 0.3 eV. The energy level bending of C60 significantly increases to ∼0.8 eV upon exposure to water moisture or oxygen gas at 5 × 10–6 Torr for 30 min. The results suggest the formation of electron traps at the C60/BCP interface upon water or moisture exposure. The decrease in electron transporting barrier between the lowest unoccupied molecular orbital (LUMO) of C60 and metal-induced gap states in BCP upon metal deposition encourages the charge leakage from cathode to C60. Charge recombination in C60 upon water or oxygen exposure is also discussed.
In article number 1606909, Ming‐Fai Lo, Chun‐Sing Lee, and co‐workers report unusual free‐carrier generation in some bipolar organic materials (SubNc and SubPc) upon photoexcitation. Single‐layer ...devices with SubNc or SubPc sandwiched between two electrodes can give power conversion efficiencies 30 times higher than previously reported single‐layer devices. Interestingly, these photoactive layers can be stacked onto each other with any sequence to generate a photocurrent in OPV devices.
Methylammonium (CH3NH3+) and formamidinium ((NH2)2CH+) based lead iodide perovskites are currently the two commonly used organic–inorganic lead iodide perovskites. There are still no alternative ...organic cations that can produce perovskites with band gaps spanning the visible spectrum (that is, <1.7 eV) for solar cell applications. Now, a new perovskite using large propane‐1,3‐diammonium cation (1,3‐Pr(NH3)22+) with a chemical structure of (1,3‐Pr(NH3)2)0.5PbI3 is demonstrated. X‐ray diffraction (XRD) shows that the new perovskite exhibits a three‐dimensional tetragonal phase. The band gap of the new perovskite is about 1.6 eV, which is desirable for photovoltaic applications. A (1,3‐Pr(NH3)2)0.5PbI3 perovskite solar cell (PSC) yields a power conversion efficiency (PCE) of 5.1 %. More importantly, this perovskite is composed of a large hydrophobic cation that provides better moisture resistance compared to CH3NH3PbI3 perovskite.
Groß und stabil: Der Perowskit (1,3‐Pr(NH3)2)0.5PbI3 wurde hergestellt. Er hat ein 3D‐Struktur und eine Bandlücke von ungefähr 1.6 eV, die das sichtbare Spektrum für Anwendungen in Solarzellen abdeckt. Durch das große Propan‐1,3‐diammonium‐Kation (1,3‐Pr(NH3)22+) ist die Substanz wasserbeständiger als CH3NH3PbI3‐Perowskite.
Hybridization between the charge transfer (CT) state of a donor–acceptor pair and lowest exciton state of the donor or the acceptor is reported to be effective for reducing recombination loss in ...organic photovoltaic (OPV) devices. Although this approach shows great success in maximizing open circuit voltage (Voc), it is typically accompanied by low device performance. Here, “complete boron sub‐(na)phthalocyanine devices” with strong hybridization resulting in lower recombination loss (≈0.47 eV) while not penalizing charge separation dynamics (internal quantum efficiency (IQE) > 80% and fill factor (FF) > 70%) are reported. Interestingly, when boron sub‐(na)phthalocyanine is paired with any other active material used in this study (“partial boron sub‐(na)phthalocyanine device”), recombination losses are still consistently maintained at lower levels (<0.53 eV). These observations denote the capability of boron sub‐(na)phthalocyanine to result in lower recombination loss devices while pairing with other materials. Special intrinsic characteristics of these materials (high dielectric constant, sharp absorption edge, unusually high absorption coefficient) and hybridization collectively result in reduced recombination loss and efficient charge generation in these systems.
Boron sub‐(na)phthalocyanine chloride–based organic photovoltaic devices exhibit extremely low recombination loss (≈0.50 eV) while not penalizing charge separation (internal quantum efficiency > 80%). Unique intrinsic properties of these materials and hybridization collectively result in low recombination loss and effective charge separation at the same time.
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► ITO/graphene oxide (GO) substrate without further treatment is used as substrate. ► ITO/GO substrate enhances the grain size and the optical absorption of CuPc films. ► PCE of GO ...buffered device shows about 30% enhancements. ► Stability of the GO buffered device are greatly enhanced.
Graphene and graphene oxide (GO) have been applied in flexible organic electronic devices with enhanced efficiency of polymeric photovoltaic (OPV) devices. In this work, we demonstrate that storage/operation stability of OPV can be substantially enhanced by spin-coating a GO buffer layer on ITO without any further treatment. With a 2nm GO buffer layer, the power conversion efficiency (PCE) of a standard copper phthalocyanine (CuPc)/fullerene (C60) based OPV device shows about 30% enhancement from 1.5% to 1.9%. More importantly, while the PCE of the standard device drop to 1/1000 of its original value after 60-days of operation-storage cycles; those of GO-buffered device maintained 84% of initial PCE even after 132-days. Atomic force microscopy studies show that CuPc forms larger crystallites on the GO-buffered ITO substrate leading to better optical absorption and thus photon utilization. Stability enhancement is attributed to the diffusion barrier of the GO layer which slow down diffusion of oxygen species from ITO to the active layers.
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► Six pairs of exciplex-forming organic materials were examined. ► All exciplex-forming pairs show depletion of mobile carriers at the junctions. ► The relation between the depletion ...organic HJs and exciplex emission is discussed.
Exciplex emission is a special form of luminescence from excited state complex formed between two contacting materials at interface in organic light-emitting devices (OLEDs). While considerable works has been focused on the role of exciplex states in interfacial light emitting processes, the understanding for the fundamental forming criteria of exciplex states is limited. In this work, six pairs of exciplex-forming organic materials were examined using photoemission spectroscopies. Interestingly, all the studied pairs show special charge transfer with N-type material donates a considerable amount of electron to the contacting P-type material, leading to energy levels bending and depletion of mobile majority carriers on the two sides of the junction, i.e. Pδ−–Nδ+. The close relation between the depletion organic HJs and the exciplex emission is discussed.
Two highly fluorescent triphenylamines (TPA) end-capped respectively with one and three pyrene arms, namely
N
,
N
-diphenyl-4-(pyren-1-yl)aniline (PyTPA) and 4,4′,4′′-trispyrenylphenylamine (TPyPA), ...have been designed, synthesized and applied as hole-transporting emitters in organic light-emitting devices (OLEDs). While the two compounds have similar chemical structures (the only difference being the number of pyrene arms), devices based on them show distinct electroluminescent characteristics. PyTPA-based devices exhibit intense deep-blue emission with Commission Internationale de L'Eclairage coordinates (CIE) of (0.14, 0.11); whilst TPyPA-based devices emit white light with CIE of (0.31, 0.35). It is considered that the three electron-donating pyrene arms in TPyPA increase its electron-donating ability, which facilitates exciplex formation with the electron-transporter. This gives rise to a yellow exciplex emission and thus shifts the electroluminescence from deep-blue to white. More importantly, both devices can operate at record-low driving voltages (<4V at 20 mA cm
−2
), indicating the TPA-cored emitters offer not only high luminance efficiencies, but also good hole-injection and transporting features.
OLEDs based on two triphenylamine derivatives show distinct electroluminescence characteristics. PyTPA devices exhibit intense deep-blue emission with CIE of (0.14, 0.11); whilst TPyPA devices emit white light with CIE of (0.31, 0.35).
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•Solid-state DSSCs have reported performance lower than that of liquid-state.•Energy band structure of FTO/TiO2/N179/spiro-OMeTAD interface is studied.•Surface dipole is observed at ...N719/spiro-OMeTAD interface.•This results in electronic mismatch in hole-collection.
Fully solid-state dye-sensitized solar cell (DSSC) has attracted much recent attention. While the origins of the lower performance in DSSC using solid electrolyte are not fully understood, there is so far no report on their interfacial electronic structures. Here, we report the charge exchange and interfacial energetics in a standard solid-state DSSC with a structure of FTO/TiO2/cis-disothiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) bis-(tetrabutylammonium) (N179 dye)/2,2,7,7-tetrakis-(N,N-di-pmethoxyphenyl-amine) 9,9-spirobifluorene (spiro-OMeTAD). While the electron-extracting barrier at TiO2/N719 interface is negligibly small (0.19eV); the abrupt vacuum levels (VLs) offsets at N719/spiro-OMeTAD interfaces results in large hole-extracting barrier of 0.43eV. Our results suggest an electronic mismatch in charge collection using spiro-OMeTAD as the hole-conducting material.
The defect state distribution for devices prepared with different idling time from BPhen to Mg:Ag deposition. Display omitted
•Idling time, a long ignored parameter is shown to influence OPV ...performance.•Metal atom penetration through BPhen decreases with increasing idling time.•These are attributed to the slow process of ‘self-reorganization’ of BPhen layer.
Deposition of metal cathode in organic photovoltaic (OPV) devices is known to cause serious metal atom penetration into the active layers and as a remedy, exciton blocking layer (EBL) is implemented. It is found that the metal penetration through EBL can be controlled by optimizing the idling time between the depositions of EBL and cathode layers. Both electrical and optical data show that the resistance of BPhen layer (EBL) to metal (Mg:Ag) penetration increase with increasing idling time. Also, significant variation in power conversion efficiency (PCE) is observed in subphthalocyanine chloride (SubPc)/fullerene (C60) based organic photovoltaic (OPV) cells by simply adding idling time as an additional control parameter. Device with optimized BPhen thickness and idling time resulted in a PCE of 2.8% whereas that of no idling time consideration has PCE limited at 2.3%. These observations are attributed to slow processes of self-organization in BPhen after their depositions.
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