Improved Film Morphology Research Articles

Synergic Surface Modifications of PbS Quantum Dots by Sodium Acetate in Solid-State Ligand Exchange toward Short-Wave Infrared Photodetectors.

PbS quantum dots (QDs) are promising for short-wave infrared (SWIR) photodetection and imaging. Solid-state ligand exchange (SSLE) is a low-fabrication-threshold QD solid fabrication method. However, QD treatment by SSLE remains challenging in seeking refined surface passivation to achieve the desired device performance. This work investigates using NaAc in the ligand exchange process to enhance the film morphology and electronic coupling configuration of QD solids. By implementing various film and photodetector device characterization studies, we confirm that adding NaAc with a prominent adding ratio of 20 wt % NaAc with tetrabutylammonium iodide (TBAI) in the SSLE leads to an improved film morphology, reduced surface roughness, and decreased trap states in the QD solid films. Moreover, compared to the devices without NaAc treatment, those fabricated with NaAc-treated QD solids exhibit an enhanced performance, including lower dark current density (<100 nA/cm2), faster response speed, higher responsivity, detectivity, and external quantum efficiency (EQE reaching 25%). The discoveries can be insightful in developing efficient, low-cost, and low-fabrication-threshold QD SWIR detection and imager applications.

Enhancement of photodetector performance of aluminum-doped zinc oxide thin films fabricated via SILAR method: Structural, optical, and electrical analysis

This study presents a comprehensive analysis of the structural, optical, electrical, and photosensing characteristics of aluminum-doped zinc oxide (Al:ZnO) thin films, fabricated via successive ionic layer adsorption and reaction (SILAR) techniques. The Raman and X-ray diffraction (XRD) analyses validated the hexagonal wurtzite structure and revealed that Al doping enhances crystallinity and crystal growth of ZnO. The average crystallite size increased from 21.6 nm in undoped sample to 23.8 nm in 5.0 wt% Al-doped sample, while strain effects decreased from 4.67 × 10-3 to 4.36 × 10-3. Scanning electron microscopy (SEM) images revealed improved film morphology and more defined geometries with increased Al doping, while energy-dispersive X-ray analysis (EDAX) confirmed successful Al integration into the ZnO lattice. Optical analyses indicate a narrowing of the ZnO bandgap to 2.81 eV in 5.0 wt% Al:ZnO from 3.02 eV in the undoped variant, while photoluminescence (PL) peak positions remains unchanged. Time-resolved fluorescence (TRF) indicated a reduction in electron lifetime with higher Al doping. Furthermore, Hall effect assessments reveal a decrease in carrier mobility and electrical resistivity, alongside a rise in carrier concentration with higher Al content. The photodetection efficacy was substantially improved with Al doping, particularly at 2.5 wt% Al, achieving a responsivity of 42.5 × 10-2 A/W, external quantum efficiency of 99.3 %, and detectivity of 1.8 × 1011 Jones. These findings exhibit that Al-doping substantially enhances the photodetection properties of ZnO thin films.

Utilization of Polycyclic Aromatic Solid Additives for Morphology and Thermal Stability Enhancement in Photoactive Layers of Organic Solar Cells.

Volatile solid additives have emerged as a promising strategy for enhancing film morphology and promoting the power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, a series of novel polycyclic aromatic additives with analogous chemical structures, including fluorene (FL), dibenzothiophene (DBT), and dibenzofuran (DBF) derived from crude oils, are presented and incorporated into OSCs. All these additives exhibit strong interactions with the electron-deficient terminal groups of L8-BO within thebulk-heterojunction OSCs. Moreover, they demonstrate significant sublimation during thermal annealing, leading to increase free volumes for the rearrangement and recrystallization of L8-BO. This phenomenon leads to an improved film morphology and an elevated glass-transition temperature of the photoactive layers. Consequently, the PCE of the PM6:L8-BO blend has been boosted from 16.60% to 18.60% with 40 wt% DBF additives, with a champion PCE of 19.11% achieved for ternary PM6:L8-BO:BTP-eC9 OSCs. Furthermore, the prolonged shelf and thermal stability have been observed in OSCs with these additives. This study emphasizes the synergic effect of volatile solid additives on the performance and thermal stability of OSCs, highlighting their potential for advancing the field of photovoltaics.

Side‐chain symmetry‐breaking strategy on porphyrin donors enables high‐efficiency binary all‐small‐molecule organic solar cells

AbstractSide‐chain symmetry‐breaking strategy plays an important role in developing photovoltaic materials for high‐efficiency all‐small‐molecule organic solar cells (ASM OSCs). However, the power conversion efficiencies (PCEs) of ASM OSCs still lag behind their polymer‐based counterparts, which can be attributed to the difficulties in achieving favorable morphology. Herein, two asymmetric porphyrin‐based donors named DAPor‐DPP and DDPor‐DPP were synthesized, presenting stronger intermolecular interaction and closer molecular stacking compared to the symmetric ZnP‐TEH. The DAPor‐DPP:6TIC blend afforded a favorable morphology with nanoscale phase separation and more ordered molecular packing, thus achieving more efficient charge transportation and suppressed charge recombination. Consequently, the DAPor‐DPP:6TIC‐based device exhibited superior photovoltaic parameters, yielding a champion PCE of 16.62% higher than that of the DDPor‐DPP‐based device (14.96%). To our knowledge, 16.62% can be ranked as one of the highest PCE values among the binary ASM OSC filed. This work provides a prospective approach to address the challenge of ASM OSCs in improving film morphology and further achieving high efficiency via side‐chain symmetry‐breaking strategy, exhibiting great potential in constructing efficient ASM OSCs.

Highly Bright and Stable Lead-Free Double Perovskite White Light-Emitting Diodes.

Lead-free double perovskites (DPs) are emerging highly stable emitters with efficient broadband self-trapped exciton (STE) photoluminescence (PL), but their low electroluminescent (EL) efficiency is a critical shortcoming. This work promotes the external quantum efficiency (EQE) and luminance of DP-based white light-emitting diode (wLED) with a normal device structure to 0.76% and 2793cd m-2 via two modifications: This work prevents the formation of adverse metallic silver, spatially confined STE, and lowers local site symmetry in Cs2 Na0.4 Ag0.6 In0.97 Bi0.03 Cl6 DP by terbium doping; and this work develops a guest-host strategy to improve film morphology, reduce defect density, and increase carrier mobility. These alterations cause substantial increase in STE radiative recombination and charge injection efficiency of perovskite layer. Finally, pure white EL with ideal color coordinates of (0.328, 0.329) and a record-breaking optoelectronic performance is achieved by introducing additional green carbon dots in LED to fill the deficient green component.

Minimized defective trap sites in perovskite absorber films by coumarin dye for efficient and reliable perovskite solar cells

This study presents a defect passivation approach using coumarin dye (7-diethylaminobenzopyran-2-one) as a multi-functional passivating agent of perovskite films to boost power conversion efficiency (PCE) and operating stability of PSCs. The coumarin dye could offer strong interaction with under-coordinated Pb2+ and vacant I− in [PbI6] octahedral frameworks due to multiple functional groups, which could serve as potential Lewis bases or hydrogen bonding sites, as well as highly conjugated aromaticity. The incorporation of coumarin dye contributes to improved film morphology of perovskite films, leading to compact and uniform grains without compromising crystallinity. Correspondingly, enhanced carrier extraction/transport and suppressed trap-assisted recombination are promoted in the perovskite films modified with coumarin dye. As a result, the coumarin dye incorporation improved the photovoltaic performance delivering a PCE of 20.85 % in planar p-i-n PSCs. The optimized device also recorded excellent indoor photovoltaic performance (PCE = 30.35 %) under dim-light condition. Furthermore, the devices passivated with coumarin dye also maintained >90 % of their initial PCEs after exposed under continuous indoor lighting irradiation (1000 lux) in ambient atmosphere for 2000 h, exhibiting impressive reliability and practical applicability.

Effect of drying behavior-induced self-organization process on the morphology and electronic properties of conjugated polymer films

In this study, the morphology and electronic properties of semiconducting polymer films were investigated in relation to a different drying behavior induced by the spinning time variation. Morphology changes related to the decreased spinning time were evaluated for p-type (P3HT, PQT-12) and n-type (N2200, PDBPyBT) polymer films fabricated at different preparation conditions. Based on the improved morphology, OFET devices were fabricated showing a 2.5 times carrier mobility increase (0.044 ± 0.012 cm2V−1s−1 for 3 s spin to 0.018 ± 0.011 cm2V−1s−1 for 30 s spin) for P3HT films, and 3 times improvement (0.088 ± 0.023 cm2V−1s−1 for 50 s to 0.28 ± 0.017 cm2V−1s−1 for 5 s) for N2200 films. For short spinning times, the slow drying of residual solvent allowed for the self-organization of polymer chains improving the crystallinity of polymer films. The presented approach synergizes the benefits of the spin coating method, like highly controlled film uniformity and thickness, with improved film morphology provided by other methods, like drop casting, or dip-coating.

Effect of Chloride Incorporation on the Intermediate Phase and Film Morphology of Methylammonium Lead Halide Perovskites.

The influence of chloride integration on perovskite film deposition, encompassing both the structures of intermediate phases and the properties of the final films, was explored. Our methodology involved the fabrication of perovskite intermediate-phase films with varying concentrations of methylammonium chloride (MACl). Subsequently, we conducted an analysis employing X-ray diffraction and Rietveld refinement, incorporating the March-Dollase correction, to gain insights into how chloride-induced intermediate phases impact film morphology. Remarkably, a distinct preferred orientation was observed in the (020) lattice plane perpendicular to the substrate surface, and this orientation was found to be directly correlated to the MACl concentration. This distinctive arrangement of chloride-induced intermediate-phase complexes facilitated controlled crystallization, leading to highly oriented crystals and an improved film morphology. As a consequence, perovskite solar cell devices incorporating chloride-containing methylammonium lead iodide achieved a power conversion efficiency exceeding 20%. These findings suggest a crucial link between the preferred orientation observed in the final chlorine-derived perovskite films and the intermediate-phase structure formed during the initial stages of perovskite formation. These results suggest a profound impact of intermediate phase compositions and crystal structures on perovskite formation, emphasizing the importance of a comprehensive understanding of these factors to enable precise control over ideal structures and the subsequent transformation into high-quality perovskite films.

Effect of addition of indium oxide layer on all-inorganic perovskite solar cells

In perovskite solar cells, the interface plays a crucial role in photovoltaic performance because excitons dissociate and compound at the interface. In this paper, the optical absorption layer of In2O3 planar perovskite solar cells is studied, which is an efficient intermediate layer between the TiO2 electron transport layer and perovskite. The modification of the In2O3 interlayer increases the average power conversion efficiency from 6.74% to 10.68%. Based on this background, some other feature descriptions are also carried out. The results show that the photovoltaic performance can be improved by depositing the In2O3 interlayer, mainly due to the improved film morphology, reduced recombination center, bulk carrier concentration and Hall mobility. It has been shown that In2O3 can be used as an efficient interface material on all-inorganic perovskite solar cells.

High efficiency ternary organic solar cells based on two nonfused ring electron acceptors with similar molecular structure

Organic solar cells (OSCs) based on nonfused ring electron acceptors (NFREAs) have shown great potential for future commercial applications due to their reduced synthesis complexity and low cost, and ternary strategy is a promising path for further boosting the development of NFREAs-based OSCs. Herein, two NFREAs FO-4Cl and FO-N with similar molecular structure are employed to fabricate high-performance ternary OSCs via combining a commonly used polymer donor PBDB-T. The PBDB-T:FO-4Cl and PBDB-T:FO-N binary devices can exhibit PCEs of 12.05% and 11.33%, respectively. Incorporating FO-N into the binary blend PBDB-T:FO-4Cl, the PBDB-T:FO-4Cl:FO-N ternary device can achieve a significantly improved PCE of 13.15% with a Voc of 0.87 V, a Jsc of 20.59 mA/cm2 and an FF of 73.02%, which is 9% and 16% higher than the PBDB-T:FO-4Cl and PBDB-T:FO-N based binary devices, respectively. The enhanced Jsc and FF can be ascribed to the enhanced photon harvesting, improved film morphology and high and balanced charge transport. Meanwhile, the Voc of ternary devices are gradually improved after the introduction of the high-lying LUMO component FO-N, which demonstrates that the two acceptors may form alloy state in the blend system. Our results demonstrate that ternary strategy is an effective path for further boosting the performance of NFREA-based OSCs by incorporating isogenous acceptors.

All-small-molecule organic solar cells based on cyclometalated tris-Ir(III) complexes as donor materials

Cyclometalated tris-Ir(III) complexes with six-coordinated octahedral configuration are beneficial to reduce aggregation for improved film morphology in organic solar cells (OSCs). Herein, two homoleptic tris-Ir complexes of eBz3Ir and eTBz3Ir showing majority absorption from UV to light-blue range are designed as electron donor materials. Owing to the extended π-conjugation by an extra thiophene ring in each ligand, eTBz3Ir exhibits red-shifted and stronger absorption as well as better charge transport property than eBz3Ir. Therefore, when employing the fused-ring non-fullerene acceptor Y6 or L8-BO to fabricate all-small-molecule OSCs (ASMOSCs), eTBz3Ir blended devices demonstrate higher efficiency than eBz3Ir, with maximum power conversion efficiency (PCE) achieving at 9.48/7.55% for Y6 and 10.48/6.46% for L8-BO devices, respectively. To our knowledge, over 10% PCE is among the highest values for binary ASMOSCs based on organometallic Ir complexes as photovoltaic materials. Such uncompetitive solar-light absorption but relatively high PCE indicates homoleptic Ir complexes with octahedral configurations are expected as promising photoactive materials for high-efficiency ASMOSCs.

Achieved 18.9% Efficiency by Fine-Tuning Non-Fullerene Acceptor Content to Simultaneously Increase the Short-Circuit Current and Fill Factor of Organic Solar Cells.

In this study, using PM6:L8-BO as the main system and non-fullerene acceptor IDIC as the third component, a series of ternary organic solar cells (TOSCs) are fabricated. The results reveal that IDIC plays a significant role in enhancing the performance of TOSCs by optimizing the morphology of blended films and forming interpenetrating nanostructure. The improved film morphology facilitates exciton dissociation and collection in TOSCs, which causes an increase in the short-circuit current density (JSC ) and fill factor (FF). Further, by optimizing the IDIC content, the power conversion efficiency (PCE) of TOSCs reaches 18.9%. Besides, the prepared TOSCs exhibit a JSC of 27.51mAcm-2 and FF of 76.64%, which are much higher than those of PM6:L8-BO-based organic solar cells (OSCs). Furthermore, the addition of IDIC improves the long-term stability of the OSCs. Meanwhile, TOSCs with a large effective area of 1.00cm2 have been prepared, which exhibit a PCE of 12.4%. These findings suggest that modifying the amount of the third component can be a useful strategy to construct hight-efficiencyTOSCs with practical application potential.

Porphyrin-based donor with asymmetric ending groups enables 16.31% efficiency for ternary all-small-molecule organic solar cells

A great attention has been aroused by all-small-molecule organic solar cells (ASM OSCs), thanks to characteristics of small molecules such as well-defined chemical structure and excellent reproducibility between batches. However, it is such a challenge to balance the aggregation behaviors of small molecules, which causes hardship for morphology optimizing of active layers, limiting further efficiency developing for ASM OSCs. Recently, the asymmetric ending group strategy has been employed in non-fullerene acceptors (NFAs) and gained great success. Herein, enlightened by the asymmetric NFAs molecule design, two asymmetric and symmetric small molecule donors, Por-DPP-TR and PTR, were synthesized. Compared to PTR, Por-DPP-TR displays an enlarged dipole moment and enhanced crystallization property. In binary OSCs, contributing to the improved film morphology, Por-DPP-TR:6TIC-based device performed an efficiency of 13.28%. Moreover, ternary ASM OSCs were constructed by employing an isogenous porphyrin-based donor, ZnP-TSEH, and an efficiency of 16.31% was obtained thanks to the further improved carrier transfer properties as well as the well-tuned morphology of obvious bi-continuous network. As far as we know, 16.31% ranks as one of the highest PCEs for ASM OSCs.

Triplet Homoleptic Iridium(III) Complex as a Potential Donor Material for Organic Solar Cells.

Triplet photovoltaic materials have been rarely investigated in organic solar cells (OSCs) because the role and mechanism of triplet excitons are still unclear. Cyclometalated heavy metal complexes with triplet features are expected to increase exciton diffusion lengths and improve exciton dissociation in OSCs, while the power conversion efficiencies (PCEs) of their bulk-heterojunction (BHJ) OSCs are still limited to <4%. We herein report an octahedral homoleptic tris-Ir(III) complex TBz3Ir as a donor material for BHJ OSCs with a PCE of over 11%. In comparison with the planar organic TBz ligand and heteroleptic TBzIr, TBz3Ir demonstrates the highest PCE and best device stability in both fullerene- and non-fullerene-based devices, owing to the long triplet lifetime, enhanced optical absorption, increased charge transport, and improved film morphology. From transient absorption, triplet excitons were deduced to participate in the photoelectric conversion process. In particular, the more significant 3D structure of TBz3Ir induces an unusual film morphology in TBz3Ir:Y6 blends, showing obviously large domain sizes suitable for triplet excitons. Thus, a high PCE of 11.35% with a high circuit current density of 24.17 mA cm-2 and a fill factor of 0.63 is achieved for small-molecular Ir complex-based BHJ OSCs.

Modification of Two-Dimensional Tin-Based Perovskites by Pentanoic Acid for Improved Performance of Field-Effect Transistors.

Understanding and controlling the nucleation and crystallization in solution-processed perovskite thin films are critical to achieving high in-plane charge carrier transport in field-effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2-thiopheneethylammonium tin iodide ((TEA)2 SnI4 ) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI6 ]4- framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn2+ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p-channel charge carrier mobility of 0.7 cm2 V-1 s-1 , which is more than a threefold increase compared with the control device. Temperature-dependent charge transport studies demonstrate a mobility of 2.3 cm2 V-1 s-1 at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high-performance Sn-based perovskite FETs.

Oxidized Carbon Materials as Hole Transport Layers for High‐Performance Organic Photovoltaics

Organic photovoltaics (OPVs) have recently advanced as promising solar cells owing to their many advantages, including the possibility of a low‐temperature solution process, lightweight, and flexibility. In OPVs, the role of the interlayer is important for efficient charge transport from the photoactive layer to electrodes. However, as a hole‐transporting layer (HTL), molybdenum oxide and poly(3,4‐ethylenedioxythiophene)–poly(styrenesulfonate) are still used for commercialization despite their drawbacks. The development of novel materials with suitable energy levels and solvent orthogonality is required to enhance hole extraction and optimize the film morphology. Herein, oxidized carbon soot (OCS) and OCS‐functionalized octadecylamine (OCS‐ODA) nanoparticles as HTL materials are synthesized. As a large number of oxygen functional groups are produced via Hummer's method, the devices with the OCS‐ODA exhibit high hole extraction ability. The ODA long alkyl chains functionalized by facile process also improve film morphology to minimize contact resistance and charge recombination. The small‐area (SA), large‐area, and flexible (F) OPVs with OCS‐ODA show power conversion efficiencies of 15.04%, 14.57%, and 12.73%, respectively. In particular, OPVs with OCS‐ODA are further demonstrated to possess storage stability in SA‐OPVs (71% retention after 450 h) and mechanical stability in F‐OPVs (78% retention after 1000 bendings).

Minimizing the transport loss and degradation of perovskite optoelectronics via grain dimerization technique

AbstractAs a next‐generation photovoltaic device, perovskite solar cell (PSC) is rapidly emerging by its appealing properties. Nevertheless, owing to the degradation which is initiated from the grain boundaries and dangling bonds on the surface, PSC is struggling with not only power conversion efficiency (PCE) but its stability. Herein, dimerization technique using diphenyl(4‐vinylphenyl)phosphine (DVP) is suggested to heal both bulk and interfaces of the perovskite grains. Effective DVP dimerization results in the minimized‐defect perovskite and constructs strong cross‐linking networks inside the grains, enabling improved device performance, reproducibility and stability. Furthermore, hydrophobic species of DVP boost the stability against humidity, which is confirmed by the solar cell dipped in water. As a result, this work obtained PSCs with improved film morphology, reproducibility and stability by DVP dimerization, achieving 21.1% of PCE stable for 1000 h under extreme conditions (AM 1.5G and 60°C, encapsulated).image

Volatile Solvent Additives Enabling High-Efficiency Organic Solar Cells without Thermal Annealing

Additive strategy is considered to be an effective way to achieve high-efficiency organic solar cells (OSCs). However, for heat-sensitive material systems, such as D18 and its derivatives, solvent additives with high-boiling points that need to be fully removed by high-temperature annealing often fail to optimize the device performance. Herein, based on the D18-Cl:Y6-based device, we chose the volatile solvent tetrahydrofuran (THF) as the solvent additive, which can achieve effects similar to high-boiling-point additives without thermal annealing. The addition of THF effectively improves the charge transport and film morphology of the active layer, the fill factor (FF) of the device is increased from 74.20 to 75.91%, and the photoelectric conversion efficiency (PCE) is increased from 16.85 to 17.70%. Further research compared the effects of THF and its derivatives and structural analogs on the device performance and explored the effect of THF on the device performance of different material systems, and the results show that volatile solvent additives have certain generality in improving film morphology. Our results indicate that the selection of volatile solvents as solvent additives is a promising strategy that can effectively improve the performance of OSCs.

Tri‐metallic quantum dot under the influence of solvent additive for improved performance of polymer solar cells

AbstractCdTeSe colloidal quantum dot (QD) was used to enhance photon capture in thin film polymer solar cells (TFPSC). The QDs were synthesized in aqueous media from two different precursors. Bulk heterojunction (BHJ) polymer blends composed of P3HT and PCBM were used as an absorber layer of the solar cell to investigate the effect of QDs. Different concentrations of QDs were used in the polymer matrix, which significantly impacted the power conversion efficiency (PCE) of the doped devices. More device performance growth was recorded by employing a small amount of solvent additives to disperse the QDs and increase the polymer's crystallinity in the medium. Hence, the addition of 1, Chloronaphthalene (CN) solvent additive in the QD‐doped bulk heterojunction film further enhanced the overall performance of the TFPSC due to improved film morphology that has significantly influenced the charge transport processes. Consequently, the PCE of the solar cell increased by nearly 50% compared to the pristine TFPSC due to the effect of solvent additives.

Highly-sensitive organic field effect transistor sensors for dual detection of humidity and NO2

Sensors based on organic field effect transistors have attracted extensive interests, but most sensors are applied to a single analyte detection. Herein, a facile strategy was proposed to optimize the growth of active layers by regulating the thickness of vanadyl-phthalocyanine (VOPc) films and carrying out the thermal annealing. Thanks to the improved film morphology and crystal properties, the carrier mobility of transistors reached 0.15 cm2V−1s−1, humidity and nitrogen dioxide (NO2) induced multi-parameter response of transistors could be considered as an efficient sensing approach. The sensitivity of threshold voltage reached 0.59 V/% RH ranging from 42%−82% RH. In addition, the gas sensing performance was systematically studied. Sensors based on 10 nm VOPc films achieved a 4710% response to 10 ppm NO2 gas, with a theoretical limit of detection down to 125.2 ppb, and the response current was improved by two orders of magnitude under the amplification effect of transistor. The obtained gas sensors also exhibited high repeatability after being stored at 90% ambient humidity. It was concluded that different charge carrier transfer mechanism in moisture and NO2 gas provided a simple idea for tunable applications of phthalocyanine-based transistors.