Search

A new approach to control the n‐doping reaction of organic semiconductors is reported using surface‐functionalized gold nanoparticles (f‐AuNPs) with alkylthiols acting as the catalyst only upon mild thermal activation. To demonstrate the versatility of this methodology, the reaction of the n‐type dopant precursor N‐DMBI‐H with several molecular and polymeric semiconductors at different temperatures with/without f‐AuNPs, vis‐à‐vis the unfunctionalized catalyst AuNPs, was investigated by spectroscopic, morphological, charge transport, and kinetic measurements as well as, computationally, the thermodynamic of catalyst activation. The combined experimental and theoretical data demonstrate that while f‐AuNPs is inactive at room temperature both in solution and in the solid state, catalyst activation occurs rapidly at mild temperatures (~70 °C) and the doping reaction completes in few seconds affording large electrical conductivities (~10–140 S cm−1). The implementation of this methodology enables the use of semiconductor+dopant+catalyst solutions and will broaden the use of the corresponding n‐doped films in opto‐electronic devices such as thin‐film transistors, electrochemical transistors, solar cells, and thermoelectrics well as guide the design of new catalysts. [ABSTRACT FROM AUTHOR]

Reducing interface nonradiative recombination is important for realizing highly efficient perovskite solar cells. In this work, we develop a synergistic bimolecular interlayer (SBI) strategy via 4-methoxyphenylphosphonic acid (MPA) and 2-phenylethylammonium iodide (PEAI) to functionalize the perovskite interface. MPA induces an in-situ chemical reaction at the perovskite surface via forming strong P-O-Pb covalent bonds that diminish the surface defect density and upshift the surface Fermi level. PEAI further creates an additional negative surface dipole so that a more n-type perovskite surface is constructed, which enhances electron extraction at the top interface. With this cooperative surface treatment, we greatly minimize interface nonradiative recombination through both enhanced defect passivation and improved energetics. The resulting p-i-n device achieves a stabilized power conversion efficiency of 25.53% and one of the smallest nonradiative recombination induced Voc loss of only 59 mV reported to date. We also obtain a certified efficiency of 25.05%. This work sheds light on the synergistic interface engineering for further improvement of perovskite solar cells. Reducing interface nonradiative recombination is important for realizing highly efficient perovskite solar cells. Here, the authors employ a bimolecular interlayer to functionalize the perovskite interface, achieving cooperative surface treatment and certified power conversion efficiency of 25.05%. [ABSTRACT FROM AUTHOR]

Conventional spectroscopies are not sufficiently selective to comprehensively understand the behaviour of trapped carriers in perovskite solar cells, particularly under their working conditions. Here we use infrared optical activation spectroscopy (i.e., pump-push-photocurrent), to observe the properties and real-time dynamics of trapped carriers within operando perovskite solar cells. We compare behaviour differences of trapped holes in pristine and surface-passivated FA0.99Cs0.01PbI3 devices using a combination of quasi-steady-state and nanosecond time-resolved pump-push-photocurrent, as well as kinetic and drift-diffusion models. We find a two-step trap-filling process: the rapid filling (~10 ns) of low-density traps in the bulk of perovskite, followed by the slower filling (~100 ns) of high-density traps at the perovskite/hole transport material interface. Surface passivation by n-octylammonium iodide dramatically reduces the number of trap states (~50 times), improving the device performance substantially. Moreover, the activation energy (~280 meV) of the dominant hole traps remains similar with and without surface passivation. Conventional spectroscopic techniques are not sufficiently selective to follow the dynamics of trapped carriers in working perovskite solar cells. Here, authors use infrared optical activation spectroscopy to observe real time evolution of trapped carriers and compare the behaviour of trapped holes. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have demonstrated a high power conversion efficiency, however, the large energy loss due to non‐radiative recombination is the main challenge for further performance enhancement. Here, a surface treatment strategy is developed by heat‐induced decomposition of a thin interlayer 2,7‐Naphthaleneditriflate (NAP) to in situ reconstruct perovskite energetics. It is verified that the reconstructed perovskite surface energetics match better with the upper hole transport layer compared to the intrinsic condition. Spontaneous generation of n/n− homojunctions between the perovskite film bulk and the surface region promotes hole extraction, enhancing built‐in electric field, and thus significantly suppresses charge recombination at such perovskite hole‐selective heterojunctions. Moreover, the surface decomposed fluorine‐rich complexes passivate the defects and improve the crystallinity of the perovskite film. These advantages are confirmed by a remarkably improved efficiency from 20.52% for the control device to 23.37% for the treated one with excellent stability. The work provides a promising approach of in situ reconstructing perovskite surface and interface for the design of highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) suffer from significant nonradiative recombination at perovskite/charge transport layer heterojunction, seriously limiting their power conversion efficiencies. Herein, solution‐processed chromium multioxide (CrOx) is judiciously selected to construct a MAPbI3/CrOx/Spiro‐OMeTAD hole‐selective heterojunction. It is demonstrated that the inserted CrOx not only effectively reduces defect sites via redox shuttle at perovskite contact, but also decreases valence band maximum (VBM)‐HOMO offset between perovskite and Spiro‐OMeTAD. This will diminish thermionic losses for collecting holes and thus promote charge transport across the heterojunction, suppressing both defect‐assisted recombination and interface carrier recombination. As a result, a remarkable improvement of 21.21% efficiency with excellent device stability is achieved compared to 18.46% of the control device, which is among the highest efficiencies for polycrystalline MAPbI3 based n–i–p planar PSCs reported to date. These findings of this work provide new insights into novel charge‐selective heterojunctions for further enhancing efficiency and stability of PSCs. [ABSTRACT FROM AUTHOR]

Introduction of filler materials into organic solar cells (OSCs) are a promising strategy to improve device performance and thermal/mechanical stability. However, the complex interactions between the state‐of‐the‐art OSC materials and filler require careful selection of filler materials and OSC fabrication to achieve lower cost and improved performance. In this work, the introduction of a natural product betulin‐based insulating polymer as filler in various OSCs is investigated. Donor–acceptor–insulator ternary OSCs are developed with improved open‐circuit voltage (Voc) due to decreased trap‐assisted recombination. Furthermore, filler‐induced vertical phase separation due to mismatched surface energy can strongly affect charge collection at the bottom interface and limit the filler ratio. A quasi‐bilayer strategy is used in all‐polymer systems to circumvent this problem. Herein, the variety of filler materials in OSCs to biomass is broadened, and the filler strategy is made a feasible and promising strategy toward highly efficient, eco, and low‐cost OSCs. [ABSTRACT FROM AUTHOR]

Energy level alignment (ELA) at donor (D) -acceptor (A) heterojunctions is essential for understanding the charge generation and recombination process in organic photovoltaic devices. However, the ELA at the D-A interfaces is largely underdetermined, resulting in debates on the fundamental operating mechanisms of high-efficiency non-fullerene organic solar cells. Here, we systematically investigate ELA and its depth-dependent variation of a range of donor/non-fullerene-acceptor interfaces by fabricating and characterizing D-A quasi bilayers and planar bilayers. In contrast to previous assumptions, we observe significant vacuum level (VL) shifts existing at the D-A interfaces, which are demonstrated to be abrupt, extending over only 1–2 layers at the heterojunctions, and are attributed to interface dipoles induced by D-A electrostatic potential differences. The VL shifts result in reduced interfacial energetic offsets and increased charge transfer (CT) state energies which reconcile the conflicting observations of large energy level offsets inferred from neat films and large CT energies of donor - non-fullerene-acceptor systems. Energy level alignment (ELA) at donor-acceptor heterojunctions is of vital importance yet largely undetermined in organic solar cells. Here, authors determine the heterojunction ELA with (mono) layer-by-layer precision to understand the co-existence of efficient charge. [ABSTRACT FROM AUTHOR]

Plasmonic metal electrodes with subwavelength nanostructures are promising for enhancing light harvesting in photovoltaics. However, the nonradiative damping of surface plasmon polaritons (SPPs) during coupling with sunlight results in the conversion of the excited hot‐electrons to heat, which limits the absorption of light and generation of photocurrent. Herein, an energy recycling strategy driven by hot‐electron emission for recycling the SPP energy trapped in the plasmonic electrodes is proposed. A transparent silver‐based plasmonic metal electrode (A‐PME) with a periodic hexagonal nanopore array is constructed, which is combined with a luminescent organic emitter for radiative recombination of the injected hot‐electrons. Owing to the suppressed SPP energy loss via broadband hot‐electron emission, the A‐PME achieves an optimized optical transmission with an average transmittance of over 80% from 380 to 1200 nm. Moreover, the indium‐tin‐oxide‐free organic solar cells yield an enhanced light harvesting with a power conversion efficiency of 16.1%. [ABSTRACT FROM AUTHOR]

Defect passivation via additive and energetic modification via interface engineering are two effective strategies for achieving high‐performance perovskite solar cells (PSCs). Here, the synergies of pentafluorophenyl acrylate when used as additive, in which it not only passivates surface defect states but also simultaneously modifies the energetics at the perovskite/Spiro‐OMeTAD interface to promote charge transport, are shown. The additive‐induced synergy effect significantly suppresses both defect‐assisted recombination and interface carrier recombination, resulting in a device efficiency of 22.42% and an open‐circuit voltage of 1.193 V with excellent device stability. The two photovoltaic parameters are among the highest values for polycrystalline CsFormamidinium/Methylammonium (FAMA)/FAMA based n‐i‐p structural PSCs using low‐cost silver electrodes reported to date. The findings provide a promising approach by choosing the dual functional additive to enhance efficiency and stability of PSCs. [ABSTRACT FROM AUTHOR]

Polyvinylpyrrolidone (PVP) has been successfully used as the cathode interfacial layer (CIL) in organic solar cells (OSCs) for work function (WF) modification. However, detailed insight into the effect of a PVP interlayer on the physicochemical properties of the indium tin oxide (ITO) electrode in inverted OSCs (I‐OSCs) is still largely absent. Herein, the ITO/PVP interface is investigated by photoelectron spectroscopy and the mechanisms for the energy level alignment of PVP on different substrates in general are unraveled. The results indicate that the dipole formation that reduces the WF is driven by not only the directional intrinsic molecular dipole moments associated with the γ‐lactam of PVP, but also an additional dipole step with the same direction created by the image charges in the contacting (semi‐)conductor layer. In addition, high‐performance inverted OSCs (I‐OSCs) are achieved by introducing a self‐assembled ultrathin PVP layer using a simple immersion method. This work provides enhanced understanding of the PVP‐based CIL and demonstrates its great potential in I‐OSC fabrication, which can pave the way to simplified manufacturing of low‐cost and large‐area devices in organic electronic technologies. [ABSTRACT FROM AUTHOR]

Incorporation of insulating polymers or molecules into organic semiconductor films, creating so‐called diluted organic semiconductors, has been successfully used both in organic field‐effect transistors and organic light‐emitting diodes to reduce sensitivity to charge traps. However, application of this strategy in organic photovoltaics is challenging due to the complex requirements on the light‐absorbing blend layer. Herein, diluted donor–acceptor–insulator ternary organic solar cells are developed to improve mobility and decrease radiative and nonradiative recombination in the active layer. In addition, both thermal and environmental stability of the diluted ternary solar cells are enhanced. Finally, the diluted semiconductor approach enables large‐area solar cells to be fabricated where the loss in power density upon cell area upscaling is five times lower than for the equivalent binary cells. [ABSTRACT FROM AUTHOR]

Perovskite solar cells are a highly competitive candidate for next‐generation photovoltaic technology. Defects in the perovskite grain boundaries and on the film surfaces however have significant impacts on both the device efficiency and environmental stability. Herein, a strategy using organic dyes as additives to passivate the defect states and produce more n‐type perovskite films, thereby improving charge transport and decreasing charge recombination, is reported. Based on this strategy, the power conversion efficiency of the perovskite solar cell is significantly increased from 18.13% to 20.18% with a negligible hysteresis. Furthermore, the rich hydrogen bonds and carbonyl structures in the organic dye can significantly enhance device stability both in terms of humidity and thermal stress. The results present a promising pathway using abundant and colorful organic dyes as additives to achieve high‐performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

In this work, a novel lamination method employing hydrogen-bond interaction to assemble a highly conductive free standing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film as a common electrode is demonstrated in a solution processed metal-free foldable integrated photocapacitor (IPC) composed of a monolithic organic solar cell (OSC) and a capacitor. The highlights of the work are: (1) micrometer free standing PEDOT:PSS electrode is successfully laminated onto a relatively large area (1 cm2) OSCs; (2) a free standing capacitor based on the PEDOT:PSS electrode is achieved; (3) the IPC demonstrates an overall efficiency of 2% and an energy storage efficiency of 58%, which is comparable with those of IPCs based on metallic common electrodes; (4) the novel lamination method for PEDOT:PSS electrode enables free standing PEDOT:PSS broad applications in solution processed flexible organic electronics, especially tandem or/and integrated organic electronic devices. Furthermore, the IPC is foldable with excellent cycling stability (no decay after 100 recycles at 1 mA cm−2). These results indicate that free standing PEDOT:PSS film is a promising candidate as common electrodes for IPCs to break the restrictions of metal electrodes. The demonstrated lamination method will greatly extend the applications of PEDOT:PSS electrodes to large area flexible organic electronic devices. [ABSTRACT FROM AUTHOR]

A new strategy for designing ternary solar cells is reported in this paper. A low-bandgap polymer named PTB7-Th and a high-bandgap polymer named PBDTTS-FTAZ sharing the same bulk ionization potential and interface positive integer charge transfer energy while featuring complementary absorption spectra are selected. They are used to fabricate efficient ternary solar cells, where the hole can be transported freely between the two donor polymers and collected by the electrode as in one broadband low bandgap polymer. Furthermore, the fullerene acceptor is chosen so that the energy of the positive integer charge transfer state of the two donor polymers is equal to the energy of negative integer charge transfer state of the fullerene, enabling enhanced dissociation of all polymer donor and fullerene acceptor excitons and suppressed bimolecular and trap assistant recombination. The two donor polymers feature good miscibility and energy transfer from high-bandgap polymer of PBDTTS-FTAZ to low-bandgap polymer of PTB7-Th, which contribute to enhanced performance of the ternary solar cell. [ABSTRACT FROM AUTHOR]

The color of polymer solar cells using an opaque electrode is given by the reflected light, which depends on the composition and thickness of each layer of the device. Metal-oxide-based optical spacers are intensively studied in polymer solar cells aiming to optimize the light absorption. However, the low conductivity of materials such as ZnO and TiO2 limits the thickness of such optical spacers to tenths of nanometers. A novel synthesis route of cluster-free Al-doped ZnO (AZO) nanocrystals (NCs) is presented for solution processing of highly conductive layers without the need of temperature annealing, including thick optical spacers on top of polymer blends. The processing of 80 nm thick optical spacers based on AZO nanocrystal solutions on top of 200 nm thick polymer blend layer is demonstrated leading to improved photocurrent density of 17% compared to solar cells using standard active layers of 90 nm in combination with thin ZnO-based optical spacers. These AZO NCs also open new opportunities for the processing of high-efficiency color tuned solar cells. For the first time, it is shown that applying solution-processed thick optical spacer with polymer blends of different thicknesses can process solar cells of similar efficiency over 7% but of different colors. [ABSTRACT FROM AUTHOR]

Ultraviolet photoelectron spectroscopy measurements in combination with the integer charge transfer (ICT) model is used to obtain the energy-level alignment diagrams for two common types of bulk-heterojunction solar cell devices based on poly(3-hexylthiophene) or poly(2-methoxy-5-(3^\prime,7 ^\prime-dimethyl-octyloxy)-1,4-phenylene vinylene) as the donor polymer and (6,6)-phenyl-C61-butric-acid as the acceptor molecule. A ground-state interface dipole at the donor/acceptor heterojunction is present for both systems, but the origin of the interface dipole differs, quadrupole-induced in the case of poly(2-methoxy-5-(3^\prime,7 ^\prime-dimethyl-octyloxy)-1,4-phenylene vinylene), and ICT state based for poly(3-hexylthiophene). The presence of bound electron–hole charge carriers (CT states) and/or interface dipoles are expected to enhance exciton dissociation into free charge carriers, thus reducing the probability that charges become trapped by Coulomb forces at the interface followed by recombination. [ABSTRACT FROM PUBLISHER]

The cathode interface plays a critical role in achieving high‐performance fullerene/perovskite planar solar cells. Herein, the simple molecule Isatin and its derivatives are introduced at the back contact [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)/Al as a cathode modification interlayer. It is revealed that the Isatin interlayers facilitate electron transport/extraction and suppress electron recombination, attributed to the formation of negative dipole potential steps and the passivation of the interfacial trap density. The average power conversion efficiencies of the resulting devices are significantly improved by 11% from 17.68% to 19.74%, with an enhancement in all device parameters including short‐circuit current, open‐circuit voltage, and fill factor. The hysteresis index is found to disappear. In addition, such interlayer enhances device stability under ambient conditions compared to the control devices due to suppression of moisture‐induced degradation of the perovskite films. These findings provide a comprehensive understanding of the engineering of the back contact between PCBM and the metal electrode to improve efficiency and stability of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Abstract Interfacial compatibility between the electrode and organic semiconductor plays a critical role in controlling the charge transport and hence efficiency of organic solar cell. Here, we introduce a novel small-molecule zwitterionic electrolyte (S1) combined with ZnO as electron transporting interlayer employed for the inverted PTB7:PC 71 BM bulk heterojunction solar cell. The resulting device with the S1/ZnO stacked interlayer achieves a high PCE of 8.59%, obtaining a 16.2% improvement over the control device performance of 7.4% without the S1 attributed to the significant increased short-circuit current density and fill factor. The interfacial properties are investigated. It is found that the S1/ZnO interlayer possess an ultralow work function of 3.6 eV, which originates from the interfacial double dipole step induced by the zwitterionic side chain electrostatic realignment at interface. The S1/ZnO interlayer exhibits the excellent charge extraction ability, suppresses the charge recombination loss and decreases the series resistance at the active layer/electrode contact. Graphical abstract Image 1 Highlights • S1 coated ZnO layer is employed as electron transporting layer for inverted organic solar cell. • S1/ZnO stacked interlayer exhibits the excellent charge extraction ability. • ZnO/S1 stacked interlayer has an ultralow work function of 3.6 eV. • The efficiency of the device with the S1/ZnO interlayer constitutes a 16.2% improvement over that of the controlled device. [ABSTRACT FROM AUTHOR]

Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4-tert-butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices. [ABSTRACT FROM AUTHOR]

The demonstration of an efficient nanostructure that provides acceptable photoelectrochemical water splitting properties using the sun visible radiation is an appealing issue. In this connection, a new ternary nanocomposite of Ag 2 S/MoS 2 /ZnO photoanode is subsequently fabricated via hydrothermal, solvothermal and SILAR methods. Different properties of the nanocomposite are characterized by XRD, SEM, EDX, XPS, UV–Vis-IR spectroscopy and electrochemical techniques. The post-grown annealed 8-Ag 2 S/MoS 2 /ZnO photoanode exhibits a good performance with a photocurrent density of 2 mA/cm2 at a bias potential 1.23 V vs. RHE. The photocurrent of the post-grown annealed 8-Ag 2 S/MoS 2 /ZnO photoanode is 71.42 times, 40 times and 2 times higher compares to the pure ZnO, post-grown annealed MoS 2 /ZnO, and post-grown annealed 8-Ag 2 S/ZnO photoanodes, respectively. The enhanced PEC performance may originate from the combination of different effects such as the expansion of light absorption and energy band alignment (type II heterostructures), [SO 4 ] acted as a charge-transfer medium, and electrode-electrolyte interface kinetic reactions. [Display omitted] • Ag 2 S/MoS 2 /ZnO ternary nanocomposite was successfully synthesized in three steps. • This ternary photoanode greatly improved the photocurrent of the PEC water splitting. • Ag 2 S components are utilized as light-absorption sensitizers. • The sacrificial reagent electrolyte is used to study the reactions. [ABSTRACT FROM AUTHOR]

Two phase-pure nanocrystalline anatase materials differing in the exposed crystal facets (0 0 1) or (1 0 1) are studied by electrochemical impedance spectroscopy and by transient photovoltage and photocurrent decay in dye sensitized solar cells. A larger chemical capacitance, indicating larger density of states, is observed for anatase (0 0 1). The presence of deep electron traps in (0 0 1) nanosheets is further confirmed by optical (UV-Vis) and photoemission (XPS, UPS) spectra. The difference in chemical capacitance indicates a slower diffusion of electrons in the (0 0 1) anatase material, but also a higher electron lifetime compared to (1 0 1) anatase material. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hybrid HTL consists of MoS 2 nanosheets and a PEDOT derivative, which results in an obvious improvement in organic solar cells' performance. • We identified that the synergy of exfoliated-MoS 2 nanosheets and DA-P result in better hole transport and extraction through systematic investigations. • By applying a comprehensive range of spectroscopies, we discovered that the dopant is derived from the oxidation products of MoS 2 nanosheets during ultrasonic exfoliation. We report an efficient hole transporting layer (HTL) for organic solar cell (OSC) based on solution-processed organic-inorganic hybrid composed of ultrasonic-exfoliated MoS 2 nanosheets and dopamine-copolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) derivative (DA-P). The OSCs based on this new hybrid HTL show a marked performance improvement over those with single-component HTLs, and they retain up to 80% of their original power conversion efficiency after 35 days. Our investigations reveal that the boost in performance is due to a synergistic effect that improves both hole transport and extraction ability. This effect is mainly due to the doping of exfoliated-MoS 2 nanosheets on DA-P. We employ a comprehensive range of spectroscopies to uncover that the dopant is derived from the oxidation products of MoS 2 nanosheets during the ultrasonic exfoliation. Our work demonstrates an efficient hybrid HTL and offers new insights into the interaction of exfoliated-MoS 2 nanosheets and the PEDOT derivatives. [ABSTRACT FROM AUTHOR]