Phenylformamidinium-enabled quasi-2D Ruddlesden-Popper perovskite solar cells with improved stability

Two-dimensional(2D)/quasi-2D perovskite solar cells(PSCs)incorporating organic spacer cations exhibit appealing ambient stability in comparison with their 3D analogs.Most reported organic spacer cations are based on ammonium,whereas formamidinium(FA^(+))has been seldom applied despite that FA has been extensively used in high-efficiency 3D PSCs.Herein,a novel FA-based organic spacer cation,4-chloro-phenylformamidinium(CPFA^(+)),is applied in quasi-2D Ruddlesden-Popper(RP)PSCs for the first time,and methylammonium chloride(MACl)is employed to promote crystal growth and orientation of perovskite film,resulting in high power conversion efficiency(PCE)with improved stability.Upon incorporating CPFA+organic spacer cation and MACl additive,high-quality quasi-2D CPFA_(2)MA_(n-1)Pb_(n)(I_(0.857)Cl_(0.143))_(3n+1)(n=9)perovskite film forms,exhibiting improved crystal orientation,reduced trap state density,prolonged carrier lifetime and optimized energy level alignment.Consequently,the CPFA_(2)MA_(n-1)Pb_(n)(I_(0.857)Cl_(0.143))_(3n+1)(n=9)quasi-2D RP PSC devices deliver a highest PCE of 14.78%.Moreover,the un-encapsulated CPFA-based quasi-2D RP PSC devices maintain~80%of its original PCE after exceeding 2000 h storage under ambient condition,whereas the 3D MAPb I3counterparts retain only~45%of its original PCE.Thus,the ambient stability of quasi-2D RP PSC devices is improved obviously relative to its 3D MAPb I3counterpart.

Large-Area Gravure-Printed AgNWs Electrode on Water/Oxygen Barrier Substrate for Long-Term Stable Large-Area Flexible Organic Solar Cells

Large-area AgNWs electrodes(25 cm×10 cm)were fabricated through roll-to-roll printing on the polyvinyl alcohol(PVA)modified water and oxygen barrier substrate.The modification of the barrier film with PVA improved the wettability of silver nanowires on the barrier films and led to the formation of homogenous large-area AgNWs networks.The mechanical flexibility,especially the adhesion force between the silver electrode and the barrier film substrate was dramatically improved through PVA modification.The efficiency of 13.51%for the flexible OSCs with an area of 0.64 cm2 was achieved based on the PET/barrier film/PVA/AgNWs electrode.The long-term stability showed the flexible OSCs based on the PET/barrier film/PVA/AgNWs electrode have a significantly improved stability relative to the device on PET/AgNWs electrode,and comparable air stability as the rigid device with glass/ITO device.The unencapsulated devices maintained nearly 50%of the original efficiency after storage for 600 h in air.After a simple top encapsulation,the flexible devices remained at 60%of the initial efficiency after 2000 h in the air.Therefore,the flexible AgNWs electrode based on the barrier film would have the potential to improve the air storage stability of organic flexible solar cells.

Recent progress in organic solar cells(PartⅠmaterial science)

During past several years,the photovoltaic performances of organic solar cells(OSCs)have achieved rapid progress with power conversion efficiencies(PCEs)over 18%,demonstrating a great practical application prospect.The development of material science including conjugated polymer donors,oligomer-like organic molecule donors,fused and nonfused ring acceptors,polymer acceptors,single-component organic solar cells and water/alcohol soluble interface materials are the key research topics in OSC field.Herein,the recent progress of these aspects is systematically summarized.Meanwhile,the current problems and future development are also discussed.

Inkjet-Printed Organic Solar Cells and Perovskite Solar Cells: Progress,Challenges, and Prospect

In recent years,the power conversion efficiency of organic solar cells(OSCs)and perovskite(PVSCs)has increased to over 19%and25%,respectively.Meanwhile,the long-term stability of OSCs and PVSCs was also significantly improved with a better understanding of the degradation mechanism and the improvement of materials,morphology,and interface stability.As both the efficiency and lifetime of solar cells are approaching the commercialization limit,fabrication methods for large-area OSCs and PVSCs that can be directly transferred from lab to fab become essential to promote the industrialization of OSCs and PVSCs.Compared with the coating methods,inkjet printing is a mature industrial technology with the advantages of random digital patterning,excellent precision and fast printing speed,which is considered to have great potential in solar cell fabrication.Many efforts have been devoted to developing inkjet-printed OSCs and PVSCs,and much progress has been achieved in the last few years.In this review,we first introduced the working principle of inkjet printing,the rheology requirements of inks,and the behaviors of the droplets.We then summarized the recent research progresses of the inkjet-printed OSCs and PVSCs to facilitate knowledge transfer between the two technologies.In the end,we gave a perspective on inkjet-printed OSCs and PVSCs.

Self-assembled nanostructures of a series of linear oligothiophene derivatives adsorbed on surfaces

Many previous studies have shown that the molecular structures of oligothiophene derivatives including molecular skeleton and alkyl chains have a significant effect on their self-assemblies on the surface.In this work, a series of linear oligothiophene derivatives(DCV-n T-Hex, n = 3~11) modified with terminal dicyanovinyls and alkyl chains were adopted to further investigate the different assembly behaviors at liquid-solid interface by scanning tunneling microscopy(STM). Interestingly, via the hydrogen bonding and van der Waals interactions, DCV-3T-Hex formed zigzag and flower structures while DCV-n T-Hex(n = 4~11) formed lamellar structures. Density functional theory(DFT) calculations show that for the most energetically favorable configurations of DCV-n T-Hex, the different distribution of alkyl chains affected intermolecular interactions, and ultimately led to the different assembled structures. The zigzag and flower structures of DCV-3T-Hex had preferential thermodynamic stability compared to other structures of DCV-n T-Hex(n = 4~11). In addition, self-assembled nanostructures of DCV-n T-Hex molecules with even numbers(n = 4, 6, 8, 10) were overall more stable than those with odd numbers(n = 5, 7, 9,11), and the stability of the self-assembled structure was weakened with the extension of the molecular backbone, individually. The orientation of molecular alkyl chains was found to greatly affect the intermolecular interactions and thus leading to various self-assembly structures of DCV-n T-Hex(n = 3~11).

Recent progress in organic solar cells(PartⅡdevice engineering)

1 Introduction Organic solar cells(OSCs)belong to a multidisciplinary field composed of chemistry,materials science,physics,engineering,etc.For a better reviewing of this field,we briefly divide the research field of OSCs into two parts:material science and device engineering.In our previous review,the material science part of OSCs,including conjugated polymer donors and acceptors,small molecular donors and acceptors.

Controllable Photoelectric Properties of Carbon Dots and Their Application in Organic Solar Cells

Organic solar cells are a current research hotspot in the energy field because of their advantages of lightness,translucency,roll to roll printing and building integration.With the rapid development of small molecule acceptor materials with high-performance,the efficiency of organic solar cells has been greatly improved.Further improving the device efficiency and stability and reducing the cost of active layer materials will contribute to the industrial development of organic solar cells.As a novel type of carbon nanomaterials,carbon dots gradually show great application potential in the field of organic solar cells due to their advantages of low preparation cost,non-toxicity and excellent photoelectric performance.Firstly,the synthesis and classification of carbon dots are briefly introduced.Secondly,the photoelectric properties of carbon dots and their adjusting,including adjustable surface energy level structure,good film-forming performance and up/down conversion characteristics are summarized.Thirdly,based on these intrinsic properties,the feasibility and advantages of carbon dots used in organic solar cells are discussed.Fourthly,the application progress of carbon dots in the active layer,hole transport layer,electron transport layer,interface modification layer and down-conversion materials of organic solar cells is also reviewed.Finally,the application progress of carbon dots in organic solar cells is prospected.Several further research directions,including in-depth exploration of the controllable preparation of carbon dots and their application in the fields of interface layer and up/down conversion for improving efficiency and stability of device are pointed out.

ZnO Surface Passivation with Glucose Enables Simultaneously Improving Efficiency and Stability of Inverted Polymer:Non-fullerene Solar Cells

The power conversion efficiency(PCE)of polymer solar cells(PSCs)has exceeded 19%due to the rapid progress of photoactive organic materials,including conjugated polymer donors and the matched non-fullerene acceptors(NFAs).Due to the high density of oxygen vacancies and the consequent photocatalytic reactivity of ZnO,structure inverted polymer solar cells with the ZnO electron transport layer(ETL)usually suffer poor device photostability.In this work,the eco-friendly glucose(Glu)is found to simultaneously improve the efficiency and stability of polymer:NFA solar cells.Under the optimal conditions,we achieved improved PCEs from 14.77%to 15.86%for the PM6:Y6 solar cells.Such a PCE improvement was attributed to the improvement in J_(SC) and FF,which is ascribed to the smoother and more hydrophobic surface of the ZnO/Glu surface,thereby enhancing the charge extraction efficiency and inhibiting charge recombination.Besides,UV-Vis absorption spectra analysis revealed that glucose modification could significantly inhibit the photodegradation of Y6,resulting in a significant improvement in the stability of the device with 92%of its initial PCE after aging for 1250 h.The application of natural interface materials in this work brings hope for the commercial application of organic solar cells and provides new ideas for developing new interface materials.

Thermoplastic elastomer enhanced interface adhesion and bending durability for flexible organic solar cells

Stable interface adhesion and bending durability of flexible organic solar cells(FOSCs)is a basic requirement for its real application in wearable electronics.Unfortunately,the device performance always degraded during continuous bending.Here,we revealed the weak interface adhesion force between MoO_(3) hole transporting layer(HTL)and the organic photoactive layer was the main reason of poor bending durability.The insertion of an interface bonding layer with a thermoplastic elastomer,polystyrene-blockpoly(ethylene-ran-butylene)-block-polystyrene(SEBS)effectively improved the interface adhesion force of MoO_(3) HTL and the active layer and decreased the modulus,which ensured higher than 90%of the initial efficiency remaining after 10000 bending.Meanwhile,the FOSCs gave an efficiency of 14.18%and 16.15%for the PM6:Y6 and PM6:L8-BO devices,which was among the highest performance of FOSCs.These results demonstrated the potential of improving the mechanical durability of FOSCs through thermoplastic elastomer interface modification.