High colloidal stability ZnO nanoparticles independent on solvent polarity and their application in polymer solar cells

Significant aggregation between ZnO nanoparticles (ZnO NPs) dispersed in polar and nonpolar solvents hinders the formation of high quality thin film for the device application and impedes their excellent electron transporting ability. Herein a bifunctional coordination complex, titanium diisopropoxide bis(acetylacetonate) (Ti(acac)2) is employed as efficient stabilizer to improve colloidal stability of ZnO NPs. Acetylacetonate functionalized ZnO exhibited long-term stability and maintained its superior optical and electrical properties for months aging under ambient atmospheric condition. The functionalized ZnO NPs were then incorporated into polymer solar cells with conventional structure as n-type buffer layer. The devices exhibited nearly identical power conversion efficiency regardless of the use of fresh and old (2 months aged) NPs. Our approach provides a simple and efficient route to boost colloidal stability of ZnO NPs in both polar and nonpolar solvents, which could enable structure-independent intense studies for efficient organic and hybrid optoelectronic devices

Fullerene-Based Photoactive A-D-A Triads for Single-Component Organic Solar Cells: Incorporation of Non-Fused Planar Conjugated Core

Two acceptor-donor-acceptor (A-D-A) single-component (SC) photovoltaic triad molecules, P3T4Rh-C6-PC61BM and P3T4Rh-C10-PC61BM, were synthesized. A conformation-locked planar conjugated core, 1,4-bis(thiophenylphenylthiophene)-2,5-difluorophenylene (P3T4), with intrachain noncovalent coulombic interactions was coupled with two fullerene derivatives, [6,6]-phenyl-C61 butyric acid propargyl ester, via copper (I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition. The D-A separation was varied by modulating the spacer alkyl chain length (C6 and C10). Both SC triads exhibited maximum absorption by the P3T4 core at ??abs = 507-510 nm, as well as absorption by PC61BM at ???300 nm. Because of the broken conjugation between the P3T4 core and PC61BM termini, the highest occupied molecular orbital (???5.58 to ???5.59 eV) was determined by the P3T4 moiety, and the lowest unoccupied molecular orbital (???3.89 to ???3.92 eV) was determined by PC61BM in the SC structures. In diluted solution, both SC triads showed significant photoluminescence quenching, indicating efficient intramolecular charge transfer between the P3T4 and PC61BM moieties. However, the semicrystalline packing of the P3T4 core was severely disrupted by the incorporation of a bulky PC61BM moiety at each terminus, which degraded the carrier transport and diode characteristics of SC organic solar cells (SCOSCs) based on P3T4Rh-C6-PC61BM and P3T4Rh-C10-PC61BM, as indicated by poor power conversion efficiency (???0.4%). No clear spacer length effect was observed. To improve the performance of SCOSCs, a design strategy is needed that enhances the intermolecular packing and ordering of the D and A moieties, which are important prerequisites for the development of optimal SC photoactive molecules

Role of Charge-Carrier Dynamics Toward the Fabrication of Efficient Air-Processed Organic Solar Cells

Over the past couple of decades, immense research has been carried out to understand the photo-physics of an organic solar cell (OSC) that is important to enhance its efficiency and stability. Since OSCs undergoes complex photophysical phenomenon, studying these factors has led to designing new materials and implementing new strategies to improve efficiency in OSCs. In this regard, the invention of the non-fullerene acceptorshas greatly revolutionized the understanding of the fundamental processes occurring in OSCs. However, such vital fundamental research from device physics perspectives is carried out on glovebox (GB) processed OSCs and there is a scarcity of research on air-processed (AP) OSCs. This review will focus on charge carrier dynamics such as exciton diffusion, exciton dissociation, charge-transfer states, significance of highest occupied molecular orbital-offsets, and hole-transfer efficiencies of GB-OSCs and compare them with the available data from the AP-OSCs. Finally, key requirements for the fabrication of efficient AP-OSCs will be presented from a charge-carrier dynamics perspective. The key aspects from the charge-carrier dynamics view to fabricate efficient OSCs either from GB or air are provided

Path to the fabrication of efficient, stable and commercially viable large-area organic solar cells

Organic solar cells (OSCs) have reached an outstanding certified power conversion efficiency (PCE) of over 19% in single junction and 20% in tandem architecture design. Such high PCEs have emerged with outstanding Y-shaped Y6 non-fullerene acceptors (NFAs), together with PM6 electron donor polymers. PCEs are on the rise for small-area OSCs. However, large-area OSC sub-modules are still unable to achieve such high PCEs, and the highest certified PCE reported so far is ∼12% having an area of 58 cm ^2 . To fabricate efficient large-area OSCs, new custom-designed NFAs for large-area systems are imminent along with improvements in the sub-module fabrication platforms. Moreover, the search for stable yet efficient OSCs is still in progress. In this review, progress in small-area OSCs is presented with reference to the advancement in the chemical structure of NFAs and donor polymers. Finally, the life-cycle assessment of OSCs is presented and the energy payback time of the efficient and stable OSCs is discussed and lastly, an outlook for the OSCs is given

Hetero-tandem organic solar cells drive water electrolysis with a solar-to-hydrogen conversion efficiency up to 10%

A hetero-tandem organic photovoltaic (OPV) device consisting of large (PM6:IT-M) and small-bandgap (PM6:Y6) bulk-heterojunctions is developed to provide an open-circuit voltage of 1.84 V and a power-conversion-efficiency of 11.7%, which could serve as an ideal light absorber to drive water electrolysis. The fabricated OPV is combined with an electrolyzer composed of NiFeOx(OH)y and Pt electrocatalysts to demonstrate a photovoltaic electrolysis (PV-EC) system. Furthermore, the system is designed to locate the operating voltage of the OPVEC system at the maximum power point of OPV to minimize power loss. As a result, our hetero-tandem OPVEC device achieves the highest solar-to-hydrogen conversion efficiency among OPV-based systems, (up to 10%), which represents a new benchmark for OPV-based solar fuel production. Finally, a wireless monolithic organic artificial leaf is constructed for the first time, which demonstrates a stable solar hydrogen production in water

Mechanically Stable Flexible Organic Photovoltaics with Silver Nanomesh for Indoor Applications

Enhanced device performance of flexible organic solar cells (FOSCs) was achieved according to the development of organic solar cells (OSCs). OSCs are promising candidates as energy sources for low-power supply systems such as the Internet of Things (IoT) under indoor lighting environments. To apply FOSCs to flexible or wearable applications, they must be mechanically stable. In this study, we fabricated FOSCs with silver nanomesh (AgNM) as the bottom transparent conductive electrode (TCE). Instead of indium tin oxide (ITO), AgNMs were prepared using three pitches of 25, 50, and 100 mu m with a square pattern, using a poly(ethylene terephthalate) (PET) substrate. Notably, the device using AgNMs with a pitch of 25 mu m exhibited a power conversion efficiency (PCE) of 14.93% under 1 sun illumination and 17.91% under 1000 lux of light-emitting diode (LED) light conditions. Flexible devices using AgNMs maintained over 92% of their initial PCE under 1 sun illumination (PCE decreased to 12.98 from 14.04%) and over 92% when tested under 1000 lux of LED light illumination (PCE decreased to 16.57 from 17.91%) after 1000 instances of bending. These results demonstrate the advantages of using AgNMs as an alternative TCE under both 1 sun and indoor lightning environments and are promising candidates for flexible applications

Fullerene-Based Triads with Controlled Alkyl Spacer Length as Photoactive Materials for Single-Component Organic Solar Cells

Two kinds of dumbbell-shaped acceptor-donor-acceptor (A-D-A)-type triad single-component (SC) photovoltaic molecules based on a benzodithiophene-rhodanine (BDTRh) core and [6,6]-phenyl-C-61 butyric acid (PC(61)BA) termini, BDTRh-C-2-PC(61)BA and BDTRh-C-10-PC(61)BA, were synthesized by modulating the alkyl (C2 and C10) spacer lengths. Both SC photovoltaic structures had similar UV-vis spectra in solution, but BDTRh-C-10-PC(61)BA showed a significantly higher absorption coefficient as a thin film. In films, a more facile intermolecular photo-induced charge transfer was observed for BDTRh-C-10-PC(61)BA in the broad-band transient absorption measurements. BDTRh-C-10-PC(61)BA also exhibited a higher hole mobility (by 25 times) and less bimolecular recombination than BDTRh-C-2-PC(61)BA By plotting the normalized external quantum efficiency data, a higher charge-transfer state was measured for BDTRh-C-10-PC(61)BA, reducing its voltage loss. A higher power conversion efficiency of similar to 2% was obtained for BDTRh-C-10-PC(61)BA, showing higher open-circuit voltage, short-circuit current density, and fill factor than those of BDTRh-C-2-PC(61)BA devices. The different carrier dynamics, voltage loss, and optical and photoelectrical characteristics depending on the spacer length were interpreted in terms of the film morphology. The longer decyl spacer in BDTRh-C-10-PC(61)BA afforded a significantly enhanced intermolecular ordering of the p-type core compared to BDTRh-C-2-PC(61)BA, suggesting that the alkyl spacer length plays a critical role in controlling the intermolecular packing interaction

High-Crystalline Regioregular Polymer Semiconductor by Thermal Treatment for Thickness Tolerance Organic Photovoltaics

To successfully develop a regioregular polymer, poly[4,8-bis(5-(2-hexyldecyl)thiophen-2-yl)benzo[1,2-b:4,5-b ']dithiophene][5,5 '-bis(7-(4-(2-butyloctyl)thiophen-2-yl)-6-fluorobenzo[c][1,2,5]thiadiazol-4-yl)-2,2 '-bithiophene] (PDBD-FBT), a symmetric monomer synthesized in high yield by tin homo-coupling reactions. PDBD-FBT is suitable as a donor material in organic photovoltaics (OPVs) because it shows high crystallinity and strong face-on packing properties. These properties were amplified by thermal annealing (TA). This causes a power conversion efficiency (PCE) enhancement in PDBD-FBT-based OPVs. Using PDBD-FBT as a polymer donor and 2,2 '-((2Z,2 ' Z)-((12,13-bis(2-heptylundecyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2 '',3 '':4 ',5 ']thieno[2 ',3 ':4,5]pyrrolo[3,2-g]thieno[2 ',3 ':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6-HU) as an electron acceptor, a PCE of 7.91% was achieved without any additive and TA at optimized active layer film thickness of approximately 100 nm. After TA, a PCE of 12.53% was achieved with a 58% increase compared with the reference devices. Owing to the strong crystallinities, trap-assisted recombination occurs by excessively formed grain boundaries; however, efficient exciton dissociation sufficiently covers these drawbacks. Even in the approximately 340 nm-thick film condition, this tendency is more pronounced (73% PCE enhancement is observed from 6.17% to 10.69% of PCE in the without and with TA devices, respectively). Our study demonstrates that it is possible to manufacture thickness-insensitive OPVs based on regioregular polymers with strong crystallinity and face-on characteristics, thereby providing a solution to the thickness variation of large-area organic solar cell modules

Coordination modulated passivation for stable organic-inorganic perovskite solar cells

Despite the recent exceptional rise in power conversion efficiency of perovskite solar cells (PSCs), surface defects and ion migration related instability are still present in PSCs. The chain length and binding energy of the passivation material play important roles in defect passivation, ion migration, moisture stability, and device-performance improvement. We synthesized three sulfonated ammonium compounds and investigated the ef-fect of post-passivation with these compounds on ion-migration and stability. New materials with high binding energy include octylamine (OA) functionalized with sulfanilic acid (OAS), p-toluenesulfonic acid (OAT), and camphorsulfonic acid (OAC). The passivation improves power conversion efficiency (PCE) from 21.06% for the control to 24.37% for the devices treated with OAC. The champion device's hysteresis index decreased to 0.01 compared to 0.11 for the control device, which is the lowest reported so far. Furthermore, the passivated perovskite films retain over 85% of their initial PCE under 60% relative humidity for 1,600 h, and the device with OAC maintains over 90% of its initial operational long-term device stability without encapsulation for 600 h under 1 sun-illumination

Effect of Substituents of Thienylene-Vinylene-Thienylene-Based Conjugated Polymer Donors on the Performance of Fullerene and Nonfullerene Solar Cells

Semiconducting polymers consisting of (E)-1,2-di(thiophen-2-yl)ethene (TVT) derivatives and benzo[1,2-b:4,5-b']-dithiophene with conjugated thiophene side chains (BDTT) were designed and synthesized to investigate the effect of fluorine and cyano groups in the 3-position of the thiophene ring in TVT on the photovoltaic properties. The corresponding PBDTT-TVT, PBDTT-FTVT, and PBDTT-CNTVT copolymers containing TVT, difluoro TVT (FTVT), and dicyano TVT (CNTVT), respectively, demonstrated considerable variations in optical, electrochemical, morphological, and charge transporting properties. PBDTT-FTVT showed suitable frontier orbital energy levels, favorable face-on orientation, and a well-mixed and smooth morphology in the blends with 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) and [6,6]-phenyl-C-71-butyric acid methyl ester (PCBM). In contrast, PBDTT-CNTVT showed unfavorable frontier orbital energy levels and bimodal orientation in the thin-film state, which interrupted efficient charge transport in organic photovoltaic devices. The device fabricated using PBDTT-FTVT exhibited the highest power conversion efficiency (PCE) of up to 6.50% with ITIC and a slightly lower PCE of 6.35% with PCBM