Rui Zhu

Visibly transparent polymer solar cells produced by solution processing.

Visibly transparent photovoltaic devices can open photovoltaic applications in many areas, such as building-integrated photovoltaics or integrated photovoltaic chargers for portable electronics. We demonstrate high-performance, visibly transparent polymer solar cells fabricated via solution processing. The photoactive layer of these visibly transparent polymer solar cells harvests solar energy from the near-infrared region while being less sensitive to visible photons. The top transparent electrode employs a highly transparent silver nanowire-metal oxide composite conducting film, which is coated through mild solution processes. With this combination, we have achieved 4% power-conversion efficiency for solution-processed and visibly transparent polymer solar cells. The optimized devices have a maximum transparency of 66% at 550 nm.

Fused Silver Nanowires with Metal Oxide Nanoparticles and Organic Polymers for Highly Transparent Conductors

Silver nanowire (AgNW) networks are promising candidates to replace indium-tin-oxide (ITO) as transparent conductors. However, complicated treatments are often required to fuse crossed AgNWs to achieve low resistance and good substrate adhesion. In this work, we demonstrate a simple and effective solution method to achieve highly conductive AgNW composite films with excellent optical transparency and mechanical properties. These properties are achieved via sequentially applying TiO(2) sol-gel and PEDOT:PSS solution to treat the AgNW film. TiO(2) solution volume shrinkage and the capillary force induced by solvent evaporation result in tighter contact between crossed AgNWs and improved film conductivity. The PEDOT:PSS coating acts as a protecting layer to achieve strong adhesion. Organic photovoltaic devices based on the AgNW-TiO(2)-PEDOT:PSS transparent conductor have shown comparable performance to those based on commercial ITO substrates.

A Robust Inter‐Connecting Layer for Achieving High Performance Tandem Polymer Solar Cells

IO N Recently, polymer solar cells (PSCs) have attracted much attention primarily due to their potential for fabricating low-cost and large-area fl exible solar cells. [ 1–3 ] Smart chemistry can design conjugated polymeric structures for PSCs with enhanced opencircuit voltage ( V OC ) and short-circuit current density ( J SC ). This has resulted in signifi cant effi ciency enhancements in recent years. Nonetheless, most of the materials designed today always suffer from the inherent disadvantage of not having a broad absorption range, which limits the utilization of the full solar spectrum. [ 4 , 5 ] A possible solution is to stack multiple photoactive layers wherein the photoactive layers have complementary absorption. Recently, multiple-junction tandem PSCs with various confi guration have been demonstrated, in which two polymer:fullerene bulk heterojunctions (BHJs) are connected in series or parallel to fulfi ll this goal. [ 6–8 ] These confi gurations enable reduction of potential loss during photon-to-electron conversion process, and add-up of electrical potential or photocurrent of the individual BHJs, while the combination of polymers with complimentary bandgaps broadens absorption band ranging 300 nm up to 900 nm, covering a larger portion of the solar spectrum. Recently, a 7.7% PCE from small organic molecule-based tandem solar cells has been achieved. [ 9 ] It strongly indicats that tandem structure is one of the promising approaches to break though 10% theoretical limit for singlejunction-based polymer solar cells. [ 10 ]

Engineering of Electron-Selective Contact for Perovskite Solar Cells with Efficiency Exceeding 15%

The past 5 years have witnessed the rise of highly efficient organometal halide perovskite-based solar cells. In conventional perovskite solar cells, compact n-type metal oxide film is always required as a blocking layer on the transparent conducting oxide (TCO) substrate for efficient electron-selective contact. In this work, an interface engineering approach is demonstrated to avoid the deposition of compact n-type metal oxide blocking film. Alkali salt solution was used to modify the TCO surface to achieve the optimized interface energy level alignment, resulting in efficient electron-selective contact. A remarkable power conversion efficiency of 15.1% was achieved under AM 1.5 G 100 mW · cm(-2) irradiation without the use of compact n-type metal oxide blocking layers.

Silver Nanowire Composite Window Layers for Fully Solution‐Deposited Thin‐Film Photovoltaic Devices

A silver nanowire-indium tin oxide nanoparticle composite and its successful application to fully solution processed CuInSe(2) solar cells as a window layer are demonstrated, effectively replacing the traditionally sputtered both intrinsic zinc oxide and indium tin oxide layers. The devices utilizing the nanocomposite window layer demonstrate photovoltaic parameters equal to or even beyond those with sputtered intrinsic zinc oxide and indium tin oxide contacts.

Solution-processed flexible transparent conductors composed of silver nanowire networks embedded in indium tin oxide nanoparticle matrices

Although silver nanowire meshes have already demonstrated sheet resistance and optical transmittance comparable to those of sputter-deposited indium tin oxide thin films, other critical issues including surface morphology, mechanical adhesion and flexibility have to be addressed before widely employing silver nanowire networks as transparent conductors in optoelectronic devices. Here, we demonstrate the efficacy of low temperature solution-processed flexible metal nanowire networks embedded in a conductive metal oxide nanoparticle matrix as transparent conductors, and investigate their microstructural, optoelectronic, and mechanical properties in attempting to resolve nearly all of the technological issues imposed on silver nanowire networks. Surrounding silver nanowires by conductive indium tin oxide nanoparticles offers low wire to wire junction resistance, smooth surface morphology, and excellent mechanical adhesion and flexibility while maintaining the high transmittance and the low sheet resistance. In addition, we discuss the relationship between sheet resistance and transmittance in the silver nanowire composite transparent conductors and their maximum achievable transmittance. Although we have selected silver nanowires and indium tin oxide nanoparticle matrix as demonstration materials, we anticipate that various metal nanowire meshes embedded in various conductive metal oxide nanoparticle matrices can effectively serve as transparent conductors for a wide variety of optoelectronic devices owing to their superior performance, simple, cost-effective, and gentle processing.Graphical abstract

Efficient perovskite solar cells by metal ion doping

Realizing the theoretical limiting power conversion efficiency (PCE) in perovskite solar cells requires a better understanding and control over the fundamental loss processes occurring in the bulk of the perovskite layer and at the internal semiconductor interfaces in devices. One of the main challenges is to eliminate the presence of charge recombination centres throughout the film which have been observed to be most densely located at regions near the grain boundaries. Here, we introduce aluminium acetylacetonate to the perovskite precursor solution, which improves the crystal quality by reducing the microstrain in the polycrystalline film. At the same time, we achieve a reduction in the non-radiative recombination rate, a remarkable improvement in the photoluminescence quantum efficiency (PLQE) and a reduction in the electronic disorder deduced from an Urbach energy of only 12.6 meV in complete devices. As a result, we demonstrate a PCE of 19.1% with negligible hysteresis in planar heterojunction solar cells comprising all organic p and n-type charge collection layers. Our work shows that an additional level of control of perovskite thin film quality is possible via impurity cation doping, and further demonstrates the continuing importance of improving the electronic quality of the perovskite absorber and the nature of the heterojunctions to further improve the solar cell performance.

Polarizing Organic Photovoltaics

Today’s most prevalent information display technology is the liquid crystal display (LCD). Unfortunately, LCDs are energy ineffi cient, as most of the backlight energy (around 75%) is lost to the orthogonal polarizers. Here, we demonstrate a novel energy recycling concept called polarizing organic photovoltaics (ZOPVs), which can potentially boost the function of an LCD by working simultaneously as a polarizer, a photovoltaic device and an ambient light or sunlight photovoltaic panel. The ZOPV fi lm was created by the uniaxial orientation of an organic conjugated polymer. A novel inverted quasibilayer structure was used to produce ZOPV devices. Signifi cant anisotropic optical and photovoltaic effects were obtained, indicating the great potential of ZOPV as a promising green technology. As an electromagnetic wave (EM), light can be divided into two linear oscillation components: the parallel (//) and perpendicular (⊥) polarizations. [ 1 ] They can be separated by a linear polarizer to provide linear polarized light, [ 2 ] and have vast applications. One of the most prevalent applications is for LCD technology. [ 3 ] Figure 1 a shows schematically the construction of LCD panels. The fundamental principle underpinning LCD operation is the modulation of light using a combination of two orthogonal polarizers with liquid crystal molecules between these two polarizers to form light valves. Currently, the most commonly used linear polarizer is the absorptive polarizer, which absorbs and wastes the unwanted polarization component while allowing the other component to be transmitted. From an energy point of view, these absorptive polarizers in LCDs are rather ineffi cient as far as the usage of the backlight photons is concerned. The power consumption of the backlight units takes up approximately 80–90% of the total power consumption in LCD modules. [ 4 ] Unfortunately, most of the backlight energy is lost to these absorptive polarizers (75%). This loss is at a maximum when the pixel displays the color black (this is when the polarizers are completely crossed), since the backlight is still fully on. In this work, we innovate on the biggest energy loss component, the polarizers, by turning the polarizer into an energy-generating photovoltaic (PV) unit, creating a polarizing organic photovoltaic device (we use the acronym ZOPV in this manuscript rather than POPV, which is often used to refer to polymer organic photovoltaics). A unique advantage of the organic conjugated materials is that the molecular chains can be easily oriented, leading to anisotropic response to polarized incident light. [ 5–8 ] This feature makes organic PV systems superior to inorganic PV or organic-hybrid PV systems [ 9 ] for the purpose of polarizing PV. ZOPV devices integrated into an LCD panel (Figure 1 b) have three potential benefi ts: i) polarization, whereby the EM wave component with an electric fi eld perpendicular to the oriented molecular chain ( s -mode polarized light [ 7 ] ) propagates through the fi lm without absorption, serving its conventional role in LCDs; ii) as a PV device, the ZOPV fi lm harvests the EM wave component parallel to the molecular chain orientation ( p -mode polarized light, which is absorbed and wasted in a conventional LCD), converting it into electricity; and iii) ambient light or sunlight PV panel, when the ZOPV device is integrated into the LCD panel, its photovoltaic function remains even when the LCD panel is not in use, producing electricity through conversion of photons from ambient light or sunlight. [ 10 ]

Anatase mesoporous TiO2 nanofibers with high surface area for solid-state dye-sensitized solar cells.

Mesoporous nanofibers (NFs) with a high surface area of 112 m(2)/g have been prepared by electrospinning technique. The structures of mesoporous NFs and regular NFs are characterized and compared through scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and selected area electron diffraction (SAED) studies. Using mesoporous TiO(2) NFs as the photoelectrode, solid-state dye-sensitized solar cells (SDSCs) have been fabricated employing D131 as the sensitizer and P3HT as the hole transporting material to yield an energy conversion efficiency (η) of 1.82%. A J(sc) of 3.979 mA cm(-2) is obtained for mesoporous NF-based devices, which is 3-fold higher than that (0.973 mA cm(-2)) for regular NF-based devices fabricated under the same condition (η = 0.42%). Incident photon-to-current conversion efficiency (IPCE) and dye-desorption test demonstrate that the increase in J(sc) is mainly due to greatly improved dye adsorption for mesoporous NFs as compared to that for regular NFs. In addition, intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) measurements indicate that the mesopores on NF surface have very minor effects on charge transport and collection. Initial aging test proves good stability of the fabricated devices, which indicates the promise of mesoporous NFs as photoelectrode for low-cost SDSCs.

Facile construction of nanofibrous ZnO photoelectrode for dye-sensitized solar cell applications

A facile method to prepare nanofibrous ZnO photoelectrodes with tunable thicknesses by electrospinning is reported. A “self-relaxation layer” is formed spontaneously between ZnO nanofibers and fluorine-doped SnO2 (FTO) substrate, which facilitates the release of interfacial tensile stress during calcination, resulting in good adhesion of ZnO film to FTO substrate. Dye-sensitized solar cells (DSSCs) based on the nanofibrous ZnO photoelectrodes are fabricated and an energy conversion efficiency of 3.02% is achieved under irradiation of AM 1.5 simulated sunlight with a power density of 100u2002mWu2009cm−2, which shows good promise of electrospun nanofibrous ZnO as the photoelectrode in DSSCs.