Shudi Lu

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%.

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.

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.

Turning a disadvantage into an advantage: synthesizing high-quality organometallic halide perovskite nanosheet arrays for humidity sensors

Though power conversion efficiencies of perovskite solar cells of over 21% have been reported, the degradation of the performance of these cells in the presence of moisture still inhibits the commercialization of these otherwise promising devices. Herein, we decided to utilize the moisture sensitivity of perovskite materials and fabricate a moisture detector based on high-quality CH3NH3PbI3−xClx nanosheet arrays. The resulting devices present a high sensitivity towards humidity with device resistance significantly dropping from 1.28 × 108 Ω at 30% relative humidity (RH) to 7.39 × 104 Ω at 90% RH and a response even faster than that of the commercial psychrometer. This response was even steeper than those of commercial psychrometers. Moreover, our device showed good reversibility and impressive specificity. Thus, the humidity sensitivity of perovskites, while disadvantageous for solar cell applications, was found to be quite applicable in a new field.

Hybrid silicon nanocone–polymer solar cells based on a transparent top electrode

Instead of using a metal grid line as the top electrode for Si nanocone/PEDOT:PSS hybrid solar cells, herein we utilize a fully covered thin layer of transparent MoO3/Ag/ZnS to efficiently collect photo-generated charge carriers without sacrificing photon absorption. Vertical silicon nanocone (SiNC) arrays with short cone lengths are prepared by a metal-assisted chemical etching technique. Such a unique structure favors the subsequent infiltration of PEDOT:PSS into the nanocone array. In addition to decent antireflection and light trapping properties, which can be attributed to the nanostructure array, the power conversion efficiency (PCE) of the hybrid solar cells reaches 5.12% upon optimizing the length of the nanocone and the thickness of the PEDOT:PSS layer. This paper not only provides an elaborate investigation on Si-based hybrid solar cells, but also gives a universal methodology for the preparation of transparent electrodes for other categories of photoelectric devices.

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.

Ultra-thin ZnO film as an electron transport layer for realizing the high efficiency of organic solar cells

To overcome the limits of low charge transport efficiency and high absorption in the UV region of conventional thick ZnO layers in organic solar cells, herein we introduce an ultra-thin ZnO film (4 nm) into PBDTTT-CF:PC70BM bulk heterojunction organic solar cells, as the electron transport layer, and realize a power conversion efficiency of 7.51%, which is dramatically higher than that of a device using general ZnO film (28.1 nm). Various techniques from both steady-state and ultra-fast views reveal that the devices with an ultra-thin ZnO film (less than 10 nm) show a higher built-in potential compared to the device with a 28.1 nm ZnO film. Such an enhancement of the built-in potential could facilitate the photo-generated excitons dissociating into free charge carriers and benefit the transport of charge carriers to the electrode. Thus, we have supplied an efficient electron conducting layer not only for the photovoltaic community but also for other photoelectronic devices.