Unraveling the Molecular Size Effect on Surface Engineering of Perovskite Solar Cells.

Surface engineering in perovskite solar cells, especially for the upper surface of perovskite, is widely studied. However, most of these studies have primarily focused on the interaction between additive functional groups and perovskite point defects, neglecting the influence of other parts of additive molecules. Herein, additives with -NH3 + functional group are introduced at the perovskite surface to suppress surface defects. The chain lengths of these additives vary to conduct a detailed investigation into the impact of molecular size. The results indicate that the propane-1,3-diamine dihydroiodide (PDAI2 ), which possesses the most suitable size, exhibited obvious optimization effects. Whereas the molecules, methylenediamine dihydroiodide (MDAI2 ) and pentane-1,5-diamine dihydroiodide (PentDAI2 ) with unsuitable size, lead to a deterioration in device performance. The PDAI2 -treated devices achieved a certified power conversion efficiency (PCE) of 25.81% and the unencapsulated devices retained over 80% of their initial PCE after 600 h AM1.5 illumination.

Insights into the Influence of Work Functions of Cathodes on Efficiencies of Perovskite Solar Cells.

Though various efforts on modification of electrodes are still undertaken to improve the efficiency of perovskite solar cells, attributing to the large scope of these methods, it is of significance to unveil the working principle systematically. Herein, inverted perovskite solar cells based on indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/CH3 NH3 PbI3 /phenyl-C61-butyric acid methyl ester (PC61 BM)/buffer metal/Al are constructed. Through the choice of different buffer metals to tune work function of the cathode, the contact nature of the active layer with the cathode could be manipulated well. In comparison with the device using Au/Al as the electrode that shows an unfavorable band bending for conducting the excited electrons to the cathode, the one with Ca/Al presents a dramatically improved efficiency over 17.1%, ascribed to the favorable band bending at the interface of the cathode with the active layer. Details for tuning the band bending and the corresponding charge transfer mechanism are given in a systematic manner. Thus, a general guideline for constructing perovskite photovoltaic devices efficiently is provided.

Recent Development in ITO-free Flexible Polymer Solar Cells.

Polymer solar cells have shown good prospect for development due to their advantages of low-cost, light-weight, solution processable fabrication, and mechanical flexibility. Their compatibility with the industrial roll-to-roll manufacturing process makes it superior to other kind of solar cells. Normally, indium tin oxide (ITO) is adopted as the transparent electrode in polymer solar cells, which combines good conductivity and transparency. However, some intrinsic weaknesses of ITO restrict its large scale applications in the future, including a high fabrication price using high temperature vacuum deposition method, scarcity of indium, brittleness and scaling up of resistance with the increase of area. Some substitutes to ITO have emerged in recent years, which can be used in flexible polymer solar cells. This article provides the review on recent progress using other transparent electrodes, including carbon nanotubes, graphene, metal nanowires and nanogrids, conductive polymer, and some other electrodes. Device stability is also discussed briefly.

The Effect of UV-Ozone Treatment on the Performance of Plasmonic Organic Solar Cells.

Silver nanoparticles (Ag NPs) solution was spin-coated on indium-tin oxide (ITO) glass substrates prior to spin-coating poly(3,4-ethylenedioxythiophene):poly(styrene- sulfonate) ( PEDOT: PSS) for the plasmonic solar cells. The sequence of spin-coating of Ag and UV-ozone treatment resulted in different device performance. For devices in which Ag NPs solution was spin-coated on ITO substrates before UV-ozone treatment, power conversion efficiency increased from 3.4% to 3.7%, while the power conversion efficiency decreased if Ag NPs solution was spin-coated after UV-ozone treatment. In both cases, the short-circuit current density increased, and the open-circuit voltage remained relatively constant. The variation of power conversion efficiency mainly depended on the changing of the fill factor, which is related to film morphology of the devices. AFM measurements of PEDOT: PSS films were taken to study the influence of film morphology on device performance.

Shifting the light emitting component from core to shell: an effective approach to improve the efficiency of light-emitting diodes based on multi-junction quantum materials.

Herein, using the light emitting component as the inner shell, we construct an advanced quantum-dot-quantum-well structure, ZnCdS/CdSe/CdZnSeS/ZnS, and use it for the fabrication of a light-emitting-diode. In comparison with the device containing conventional structured quantum dots, CdSe/CdZnSeS/ZnS, the advanced device possesses a superior performance in aspects of luminance, current efficiency, turn-on voltage and emitting wavelength tunability. Therefore, this paper indicates a promising strategy for the fabrication of light emitting devices based on quantum materials.

Fully understanding the positive roles of plasmonic nanoparticles in ameliorating the efficiency of organic solar cells.

Herein, we constructed inverted PBDTTT-CF:PC70BM bulk-heterojunction organic solar cells by introducing Au nanoparticles to a ZnO buffer layer and a great improvement in energy conversion efficiency has been realized. To discover the positive roles of such plasmonic nanoparticles in the process of solar energy conversion, photovoltaic devices with the same architecture but different sized Au nanoparticles were purposely fabricated and it has been observed that the overall efficiency can be remarkably improved from 6.67% to 7.86% by embedding 41 nm Au nanoparticles in the buffer layer. The devices with other sizes of Au nanoparticles show a relatively low performance. Subsequent investigations including finite difference time domain simulation and transient photoluminescence studies reveal that the existence of the plasmonic particles could not only improve the optical absorption and facilitate the exciton separation, but can also benefit the collection of charge carriers. Thus, this paper provides a comprehensive perspective on the roles of plasmonic particles in organic solar cells and insights into the photo energy conversion process in the plasmonic surroundings.

Efficient hybrid plasmonic polymer solar cells with Ag nanoparticle decorated TiO2 nanorods embedded in the active layer.

A hybrid plasmonic polymer solar cell, in which plasmonic metallic nanostructures (such as Ag, Au, and Pt nanoparticles) are embedded in the active layer, has been under intense scrutiny recently because it provides a promising new approach to enhance the efficiency of the device. We propose a brand new hybrid plasmonic nanostructure, which combines a plasmonic metallic nanostructure and one-dimensional semiconductor nanocrystals, to enhance the photocurrent of the device through a strong localized electric field and an enhanced charge transport channel. We demonstrate that when Ag nanoparticle decorated TiO2 nanorods were introduced into the active layer of polymer-fullerene based bulk heterojunction solar cells, the photocurrent significantly increased to 14.15 mA cm(-2) from 6.51 mA cm(-2) without a decrease in the open voltage; thus, the energy conversion efficiency was dramatically enhanced to 4.87% from 2.57%.