Photochemically and Thermally Programmed Optical Multi-States from a Single Diacetylene-Functionalized Cyanostilbene Luminogen.

To develop advanced optical systems, many scientists have endeavored to create smart optical materials which can tune their photophysical properties by changing molecular states. However, optical multi-states are obtained usually by mixing many dyes or stacking multi-layered structures. Here, multiple molecular states are tried to be generated with a single dye. In order to achieve the goal, a diacetylene-functionalized cyanostilbene luminogen (DACSM) is newly synthesized by covalently connecting diacetylene and cyanostilbene molecular functions. Photochemical reaction of cyanostilbene and topochemical polymerization of diacetylene can change the molecular state of DACSM. By thermal stimulations and the photochemical reaction, the conformation of polymerized DACSM is further tuned. The synergetic molecular cooperation of cyanostilbene and diacetylene generates multiple molecular states of DACSM. Utilizing the optical multi-states achieved from the newly developed DACSM, switchable optical patterns and smart secret codes are successfully demonstrated.

Suppressing Redox Reactions at the Perovskite-Nickel Oxide Interface with Zinc Nitride to Improve the Performance of Perovskite Solar Cells.

For p-i-n perovskite solar cells (PSCs), nickel oxide (NiOx) hole transport layers (HTLs) are the preferred interfacial layer due to their low cost, high mobility, high transmittance, and stability. However, the redox reaction between the Ni≥3+ and hydroxyl groups in the NiOx and perovskite layer leads to oxidized CH3NH3 + and reacts with PbI in the perovskite, resulting in a large number of non-radiative recombination sites. Among various transition metals, an ultra-thin zinc nitride (Zn3N2) layer on the NiOx surface is chosen to prevent these redox reactions and interfacial issues using a simple solution process at low temperatures. The redox reaction and non-radiative recombination at the interface of the perovskite and NiOx reduce chemically by using interface modifier Zn3N2 to reduce hydroxyl group and defects on the surface of NiOx. A thin layer of Zn3N2 at the NiOx/perovskite interface results in a high Ni3+/Ni2+ ratio and a significant work function (WF), which inhibits the redox reaction and provides a highly aligned energy level with perovskite crystal and rigorous trap-passivation ability. Consequently, Zn3N2-modified NiOx-based PSCs achieve a champion PCE of 21.61%, over the NiOx-based PSCs. After Zn3N2 modification, the PSC can improve stability under several conditions.

Enhancing the Stability and Efficiency of Inverted Perovskite Solar Cells with a Mixed Ammonium Ligands Passivation Strategy.

The perovskite solar cell (PSC), which has achieved efficiencies of more than 26%, is expected to be a promising technology that can alternate silicon-based solar cells. However, the performance of PSCs is still limited due to defects and ion migration that occur at the large number of grain boundaries present in perovskite thin films. In this study, the mixed ammonium ligands passivation strategy (MAPS) is demonstrated, which combines n-octylammonium iodide (OAI) and 1,3-diaminopropane (DAP) can effectively suppress the grain boundary defects and ion migration through grain boundaries by the synergistic effect of OAI and DAP, resulting in improved efficiency and stability of PSCs. It has also been revealed that MAPS not only enhances crystallinity and reduces grain boundaries but also improves charge transport while suppressing charge recombination. The MAPS-based opaque PSC shows the best power conversion efficiency (PCE) of 21.29% with improved open-circuit voltage (VOC ) and fill factor (FF), and retained 84% of its initial PCE after 1900 h at 65 °C in N2 atmosphere. Amazingly, the MAPS-based semi-transparent PSC (STP-PSC) retained 94% of their maximum power (21.00% at around 10% AVT) after 1000 h under 1 sun illumination and MAPS-based perovskite submodule (PSM) achieved a PCE of 19.59%, which is among the highest values reported recently.

Chemical Bridge-Mediated Heterojunction Electron Transport Layers Enable Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) emerged as potential photovoltaic energy-generating devices developing in recent years because of their excellent photovoltaic properties and ease of processing. However, PSCs are still reporting efficiencies much lower than their theoretical limits owing to various losses caused by the charge transport layer and the perovskite. In this regard, herein, an interface engineering strategy using functional molecules and chemical bridges was applied to reduce the loss of the heterojunction electron transport layer. As a functional interface layer, ethylenediaminetetraacetic acid (EDTA) was introduced between PCBM and the ZnO layer, and as a result, EDTA simultaneously formed chemical bonds with PCBM and ZnO to serve as a chemical bridge connecting the two. DFT and chemical analyses revealed that EDTA can act as a chemical bridge between PCBM and ZnO, passivate defect sites, and improve charge transfer. Optoelectrical analysis proved that EDTA chemical bridge-mediated charge transfer (CBM-CT) provides more efficient interfacial charge transport by reducing trap-assisted recombination losses at ETL interfaces, thereby improving device performance. The PSC with EDTA chemical bridge-mediated heterojunction ETL exhibited a high PCE of 21.21%, almost no hysteresis, and excellent stability to both air and light.

Innovative Approaches to Semi-Transparent Perovskite Solar Cells.

Perovskite solar cells (PSCs) are advancing rapidly and have reached a performance comparable to that of silicon solar cells. Recently, they have been expanding into a variety of applications based on the excellent photoelectric properties of perovskite. Semi-transparent PSCs (ST-PSCs) are one promising application that utilizes the tunable transmittance of perovskite photoactive layers, which can be used in tandem solar cells (TSC) and building-integrated photovoltaics (BIPV). However, the inverse relationship between light transmittance and efficiency is a challenge in the development of ST-PSCs. To overcome these challenges, numerous studies are underway, including those on band-gap tuning, high-performance charge transport layers and electrodes, and creating island-shaped microstructures. This review provides a general and concise summary of the innovative approaches in ST-PSCs, including advances in the perovskite photoactive layer, transparent electrodes, device structures and their applications in TSC and BIPV. Furthermore, the essential requirements and challenges to be addressed to realize ST-PSCs are discussed, and the prospects of ST-PSCs are presented.

Enhanced Device Performances of MAFACsPb(IxBr1-x) Perovskite Solar Cells with Dual-Functional 2-Chloroethyl Acrylate Additives.

Perovskite photovoltaics (PePVs) tend to suffer from a high density of defects that restrict the device in terms of performances and stability. Therefore, defect passivation and film-quality improvement of perovskite active layers are crucial for high-performance PePVs. In this work, 2-chloroethyl acrylate (CEA) with C═O and -Cl groups in Cs0.175FA0.750MA0.075Pb (I0.880Br0.120) precursor solutions is introduced as a novel bifunctional additive to act as both a defect passivator and perovskite-growth controller. With the aid of CEA, the perovskite crystallinity and average grain size are improved, and perovskite defects are effectively reduced, thus increasing the representative efficiency (PCE = 19.32%). PePVs with CEA also maintain their initial efficiency of 85% even after about 500 h under air conditions with a humidity of 40 ± 5%. As a result, this study proves that the novel additive CEA can produce higher PePV efficiency and more stable devices.

Non-Fullerene Small Molecule Electron-Transporting Materials for Efficient p-i-n Perovskite Solar Cells.

PC61BM is commonly used in perovskite solar cells (PSC) as the electron transport material (ETM). However, PC61BM film has various disadvantages, such as its low coverage or the many pinholes that appear due to its aggregation behavior. These faults may lead to undesirable direct contact between the metal cathode and perovskite film, which could result in charge recombination at the perovskite/metal interface. In order to overcome this problem, three alternative non-fullerene electron materials were applied to inverted PSCs; they were evaluated on suitability as electron transport layers. The roles and effects of these non-fullerene ETMs on device performance were studied using photoluminescence (PL) measurements, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), internal resistance in PSC measurements, and conductive atomic force microscopy (C-AFM). It was found that one of the tested materials, IT-4f, showed excellent electron extraction ability and was associated with reduced recombination. The PSC with IT-4f as the ETM produced better cell-performance; it had an average PCE of 11.21%, which makes it better than the ITIC and COi8DFIC-based devices. Finally, IT-4f was compared with PC61BM; it was found that the two materials have quite comparable efficiency and stability levels.

Microstructure and chemical analysis data of polyurethane-silver nanoparticles/graphene nanoplates composite fibers.

In this data article, we provide field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) images of wet-spun polyurethane (PU)-silver nanoparticles (AgNPs)/graphene nanoplatelets (GNPs) composite fibers according to the content of AgNPs and GNPs. In addition, microstructural changes of PU-AgNPs/GNPs composite fibers due to heat treatment at various temperatures are provided. The data collected in this article is directly related to our research article "Stretchable and Electrically Conductive Polyurethane- Silver/Graphene composite fibers prepared by wet-spinning process" [1].

Structural design considerations of solution-processable graphenes as interfacial materials via a controllable synthesis method for the achievement of highly efficient, stable, and printable planar perovskite solar cells.

Solution-processable graphenes (represented by reduced graphene oxides, rGOs) have shown promising abilities as HTLs in perovskite solar cells (PeSCs). However, there has been no attempt to systematically tailor the characteristics of rGOs to the specifications of PeSCs. Furthermore, the applications of rGO HTLs have been limited to the spin-coating system, which is incompatible with roll-to-roll manufacturing. Here, with the aid of a polymer-graphene hybrid structure and a controllable synthesis method, we successfully developed a much more feasible rGO HTL and demonstrated highly efficient, stable, and printable p-i-n planar PeSCs with facile one-step processing. The characteristics of the developed polyacrylonitrile-grafted rGOs (PRGOs) were optimized by varying the synthesis conditions including the γ-radiation intensity (200, 400, and 600 kGy) and the concentration of the acrylonitrile (AN) precursor (2, 4, and 6 wt%). It is revealed that the PRGO synthesized with a lower AN concentration and a higher irradiation intensity (PRGO_2-600) is the most suitable one for PeSC HTL. PRGO_2-600 effectively raises the average power conversion efficiencies (PCEs) of PeSCs by ∼36% compared to those of conventional PeSCs using PEDOT:PSS HTL. The comprehensive investigations confirm that the enhanced device efficiency stems from (1) the favorable interlayer characteristics of the PRGO itself and (2) the well-crystallized perovskite layer grown on the PRGO. In addition to the PCE, thechemically inert PRGOs can also maintain their electrical properties over time and retard the decomposition of perovskite films, thereby prolonging the operation time of PeSCs in the atmosphere. More importantly, the applicability of the PRGO HTL is clearly verified even in the roll-to-roll compatible slot-die coating system, exhibiting comparable performances to those of the spin-coating system.

Statistical analyses on inverted perovskite solar cells employing non-fullerene-based small molecule as a cathode interfacial layer.

In this data article, we present the influences of the solvent, concentration, and spin rates of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene) (ITIC) material on the performances of perovskite solar cells (PSCs). The device parameters such as open-circuit voltage (Voc), short circuit current (Jsc), fill factor (FF), and power conversion efficiency (PCE) were measured with Keithley 2400 source meter unit under 100 mW/cm2 (AM 1.5 G). The data in this article describe the optimization of ITIC-based PSCs and are directly related to our research article "Non-fullerene-based small molecules as an efficient n-type electron transporting layers in inverted organic-inorganic halide perovskite solar cells" (Noh et al., Submitted for publication) [1].

Hysteresis data of planar perovskite solar cells fabricated with different solvents.

In this data article, we introduced the hysteresis of planar perovskite solar cells (PSCs) fabricated using dimethylformamide (DMF), gamma-butyrolactone (GBL), methyl-2-pyrrolidinone (NMP), dimethylsulfoxide (DMSO), DMF-DMSO, GBL-DMSO and NMP-DMSO as perovskite precursor solutions according to different scan directions, sweep times, and current stability. The hysteresis analyses of the planar PSCs prepared with a glass-ITO /NiOX/perovskite /PC61BM/BCP/Ag configuration were measured with Keithley 2400 source meter unit under 100 mW/cm2 (AM 1.5 G). The data collected in this article compares the hysteresis of PSCs with different solvents and is directly related to our research article "High-Performance Planar Perovskite Solar Cells: Influence of Solvent upon Performance" (You-Hyun Seo et al., 2017 [1]).

Photo-cross-linked perylene diimide derivative materials as efficient electron transporting layers in inverted polymer solar cells.

We present an efficient and stable interfacial material based on a water-soluble perylene diimide derivative functionalized with ionic and methacrylate groups (abbreviated as PDIM), which can be stabilized by the photo-polymerization of diacrylate groups at both ends of the side chain in the PDIM. The characteristics of the photo-cross-linked PDIM films were examined using absorption spectra, cyclic voltammetry, work function, and surface morphology. The feasibility of the photo-cross-linked PDIM films as a novel electron transporting layer (ETL) in polymer solar cells (PSCs) was also investigated. The PTB7-Th:PC71BM-based PSC using the PDIM as the ETL achieved the excellent power conversion efficiency of 9.44% similar to the conventional polyethylenimine ethoxylated (PEIE) and better than ZnO. Furthermore, the PSC with the PDIM films exhibited a similar lifetime to that of the PEIE-based device. This approach suggests that the photo-cross-linked PDIM film could be regarded as a promising interfacial material for fabricating highly efficient PSCs.

Synergetic effects of solution-processable fluorinated graphene and PEDOT as a hole-transporting layer for highly efficient and stable normal-structure perovskite solar cells.

We demonstrate that a bi-interlayer consisting of water-free poly(3,4-ethylenedioxythiophene) (PEDOT) and fluorinated reduced graphene oxide (FrGO) noticeably enhances the efficiency and the stability of the normal-structure perovskite solar cells (PeSCs). With simple and low temperature solution-processing, the PeSC employing the PEDOT + FrGO interlayer exhibits a significantly improved power conversion efficiency (PCE) of 14.9%. Comprehensive investigations indicate that the enhanced PCE is mostly attributed to the retarded recombination in the devices. The minimized recombination phenomena are related to the interfacial dipoles at the PEDOT/FrGO interface, which facilitates the electron-blocking and the higher built-in potential in the devices. Furthermore, the PEDOT + FrGO device shows a better stability by maintaining 70% of the initial PCE over the 30 days exposure to ambient conditions. This is because the more hydrophobic graphitic sheets of the FrGO on the PEDOT further protect the perovskite films from oxygen/water penetration. Consequently, the introduction of composite interfacial layers including graphene derivatives can be an effective and versatile strategy for high-performing, stable, and cost-effective PeSCs.

Diketopyrrolopyrrole-Based Metallated Polymer for Bulk-Heterojunction Solar Cells and Organic Field-Effect Transistors.

We report the synthesis and optoelectronic properties of novel platinum-based polymers (p-Pt-DPP) incorporating 3,6-di-2-thienyl-2,5-dihydro-2,5-diethylhexylpyrrolo[3,4-c]pyrrole-1,4-dione. The synthesized amorphous metallated polymer exhibited long wavelength absorption in the range of 500­684 nm and a band-gap as low as 1.75 eV. Organic field-effect transistors (OFETs) fabricated from p-Pt-DPP showed hole mobility of 1.6 × 10⁻³ cm² · V⁻¹s⁻¹ and an on/off ratio of 5 × 104. In addition, polymer solar cells (PSCs) based on p-Pt-DPP and PC71BM exhibited a photovoltaic efficiency of 1.22% under AM 1.5 G conditions with an illumination of 100 mW·cm−2 without any annealing process.

Tin doped indium oxide anodes with artificially controlled nano-scale roughness using segregated Ag nanoparticles for organic solar cells.

Nano-scale surface roughness in transparent ITO films was artificially formed by sputtering a mixed Ag and ITO layer and wet etching of segregated Ag nanoparticles from the surface of the ITO film. Effective removal of self-segregated Ag particles from the grain boundaries and surface of the crystalline ITO film led to a change in only the nano-scale surface morphology of ITO film without changes in the sheet resistance and optical transmittance. A nano-scale rough surface of the ITO film led to an increase in contact area between the hole transport layer and the ITO anode, and eventually increased the hole extraction efficiency in the organic solar cells (OSCs). The heterojunction OSCs fabricated on the ITO anode with a nano-scale surface roughness exhibited a higher power conversion efficiency of 3.320%, than that (2.938%) of OSCs made with the reference ITO/glass. The results here introduce a new method to improve the performance of OSCs by simply modifying the surface morphology of the ITO anodes.

Blending of n-type Semiconducting Polymer and PC61BM for an Efficient Electron-Selective Material to Boost the Performance of the Planar Perovskite Solar Cell.

The highly efficient CH3NH3PbI3 perovskite solar cell (PeSC) is simply achieved by employing a blended electron-transport layer (ETL) consisting of PC61BM and P(NDI2OD-T2). The high molecular weight of P(NDI2OD-T2) allows for a thinned ETL with a uniform morphology that optimizes the PC61BM ETL more effectively. As a result of this enhancement, the power conversion efficiency of a PC61BM:P(NDI2OD-T2)-based PeSC is 25% greater than that of the conventional PC61BM based-PeSC; additionally, the incorporation of P(NDI2OD-T2) into PC61BM attenuates the dependence of the PeSC on the ETL-processing conditions regarding its performance. It is revealed that, in addition to the desirable n-type semiconducting characteristics of PC61BM:P(NDI2OD-T2)-including a higher electron-mobility and a more-effective electron selectivity of a blended ETL for an efficient electron extraction-the superior performance of a PC61BM:P(NDI2OD-T2) device is the result of a thinned and uniformly covered ETL on the perovskite layer.

Graphene oxide/PEDOT:PSS composite hole transport layer for efficient and stable planar heterojunction perovskite solar cells.

We investigated a graphene oxide (GO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ( PEDOT: PSS) composite as a promising candidate for the practical application of a 2-D carbonaceous hole transport layer (HTL) to planar heterojunction perovskite solar cells (PeSCs) consisting of a transparent electrode/HTL/perovskite/fullerene/metal electrode. Both the insulating properties of GO and the non-uniform coating of the transparent electrode with GO cause the poor morphology of perovskite induced low power conversion efficiency (PCE) of 6.4%. On the other hand, PeSCs with a GO/PEDOT:PSS composite HTL, exhibited a higher PCE of 9.7% than that of a device fabricated with conventional PEDOT: PSS showing a PCE of 8.2%. The higher performance is attributed to the decreased series resistance (RS) and increased shunt resistance (RSh). The well-matched work-function between GO (4.9 eV) and PEDOT: PSS (5.1 eV) probably results in more efficient charge transport and an overall decrease in RS. The existence of GO with a large bandgap of ∼3.6 eV might induce the effective blocking of electrons, leading to an increase of RSh. Moreover, improvement in the long-term stability under atmospheric conditions was observed.

Efficient PEDOT:PSS-Free Polymer Solar Cells with an Easily Accessible Polyacrylonitrile Polymer Material as a Novel Solution-Processable Anode Interfacial Layer.

We demonstrate that an easily accessible polyacrylonitrile (PAN) polymer can efficiently function as a novel solution-processable anode interfacial layer (AIL) to boost the device performances of polymer:fullerene-based solar cells (PSCs). The PAN thin film was simply prepared with spin-coating of a cost-efficient PAN solution dissolved in dimethylformamide on indium tin oxide (ITO), and the thin polymeric interlayer on PSC parameters and stability were systemically investigated. As a result, the cell efficiency of the PSC with PAN was remarkably enhanced compared to the device using bare ITO. Furthermore, with PAN, we finally achieved an excellent power conversion efficiency (PCE) of 6.7% and a very high PSC stability in PTB7:PC71BM systems, which constitute a highly comparable PCE and superior device lifetime relative to those of conventional PSCs with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS). These results demonstrate that the inexpensive solution-processed PAN polymer can be an attractive PEDOT: PSS alternative and is more powerful for achieving better cell performances and lower cost PSC production.

An approach for an advanced anode interfacial layer with electron-blocking ability to achieve high-efficiency organic photovoltaics.

The interfacial properties of PEDOT:PSS, pristine r-GO, and r-GO with sulfonic acid (SR-GO) in organic photovoltaic are investigated to elucidate electron-blocking property of PEDOT:PSS anode interfacial layer (AIL), and to explore the possibility of r-GO as electron-blocking layers. The SR-GO results in an optimized power conversion efficiency of 7.54% for PTB7-th:PC71BM and 5.64% for P3HT:IC61BA systems. By combining analyses of capacitance-voltage and photovoltaic-parameters dependence on light intensity, it is found that recombination process at SR-GO/active film is minimized. In contrast, the devices using r-GO without sulfonic acid show trap-assisted recombination. The enhanced electron-blocking properties in PEDOT:PSS and SR-GO AILs can be attributed to surface dipoles at AIL/acceptor. Thus, for electron-blocking, the AIL/acceptor interface should be importantly considered in OPVs. Also, by simply introducing sulfonic acid unit on r-GO, excellent contact selectivity can be realized in OPVs.

Fluorine-functionalized and simultaneously reduced graphene oxide as a novel hole transporting layer for highly efficient and stable organic photovoltaic cells.

A one-step reduction and functionalization of graphene oxide (FrGO) was easily achieved using a novel phenylhydrazine-based reductant containing fluorine atoms, which can induce p-type doping due to its high electronegativity. The FrGO-based OPV exhibited a high power conversion efficiency of ∼6.71% and a superior OPV-stability to commercial PEDOT:PSS.