Core-shell structured photovoltaic devices based on PbS quantum dots and silicon nanopillar arrays

We fabricated three-dimensional silicon nanopillar array (SiNP)-based photovoltaic (PV) devices using PbS quantum dots (QDs) as the hole-transporting layers. The core-shell structured device, which is based on high aspect ratio SiNPs standing on roughed silicon substrates, displays a higher PV performance with a power conversion efficiency (PCE) of 6.53% compared with that of the planar device (2.11%). The enhanced PCE is ascribed to the increased light absorption and the improved charge carrier collections in SiNP-modified silicon surfaces. We also show that, for the core-shell structured device, the thickness of the shell layer plays a critical role in enhancing the PV performance and around five monolayers of QDs are preferred for efficient hole-transporting. Wafer-scale PV devices with a radial PbS/SiNP heterojunction can be fabricated by solution phase techniques at low temperatures, suggesting a facile route to fabricate unique three-dimensional nanostructured devices.     

Amorphous silicon nanocone array solar cell

ABSTRACT: In the hydrogenated amorphous silicon [a-Si:H]-thin film solar cell, large amounts of traps reduce the carrier's lifetime that limit the photovoltaic performance, especially the power conversion efficiency. The nanowire structure is proposed to solve the low efficiency problem. In this work, we propose an amorphous silicon [a-Si]-solar cell with a nanocone array structure were implemented by reactive-ion etching through a polystyrene nanosphere template. The amorphous-Si nanocone exhibits absorption coefficient around 5 × 105/cm which is similar to the planar a-Si:H layer in our study. The nanostructure could provide the efficient carrier collection. Owing to the better carrier collection efficiency, efficiency of a-Si solar cell was increased from 1.43% to 1.77% by adding the nanocone structure which has 24% enhancement. Further passivation of the a-Si:H surface by hydrogen plasma treatment and an additional 10-nm intrinsic-a-Si:H layer, the efficiency could further increase to 2.2%, which is 54% enhanced as compared to the planar solar cell. The input-photon-to-current conversion efficiency spectrum indicates the efficient carrier collection from 300 to 800 nm of incident light.     

Optical simulations of P3HT/Si nanowire array hybrid solar cells

An optical simulation of poly(3-hexylthiophene) (P3HT)/Si nanowire array (NWA) hybrid solar cells was investigated to evaluate the optical design requirements of the system by using finite-difference time-domain (FDTD) method. Steady improvement of light absorption was obtained with increased P3HT coating shell thickness from 0 to 80 nm on Si NWA. Further increasing the thickness caused dramatic decrease of the light absorption. Combined with the analysis of ultimate photocurrents, an optimum geometric structure with a coating P3HT thickness of 80 nm was proposed. At this structure, the hybrid solar cells show the most efficient light absorption. The optimization of the geometric structure and further understanding of the optical characteristics may contribute to the development for the practical experiment of the promising hybrid solar cells.     

Absorption Enhancement in Ultrathin Structures Based on Crystalline-Si/Ag Parabola Nanocones Periodic Arrays with Broadband Antireflection Property

In this study, we examine the optical properties and unique features of a novel design of a parabola nanocone consisting of a homogenous shell-like cover layer of crystalline silicon (c-Si) and an Ag core which provides an enhanced absorption efficiency and significant photocurrent conversion during exposure to an incident light. Determining the geometrical sizes of the c-Si/Ag parabola nanocone, we designed an antireflection nanostructure based on certain arrays of investigated cone arrays on a GaAs substrate. We proved that the examined nanostructure shows a low percentage of reflectance of 6.24 % and a significant short current density of ~37.2 mA/m ² as well as broadband antireflection facility. This understanding paves the way for novel methods toward the use of a simple and two layer nanoparticle in designing efficient and high performance antireflection layers of photovoltaics and solar cells that are able to function over a wide range of spectrum.     

Porous Polydimethylsiloxane/Au Composites as Solar-Light Absorbers for Light-Driven Thermoelectric Applications

Solar thermoelectric (TE) generators may potentially provide a viable alternative to photovoltaic devices for producing electrical energy from renewable sources. In this approach, the conversion of solar radiation into heat is essential to enhance the performance of TE devices, which necessitates the development of efficient solar light absorbers. Metal nanoparticles (NPs) have gained much attention in this regard because they can convert light into heat via plasmon-mediated photothermal effects. In this study, porous nanocomposites comprising polydimethylsiloxane (PDMS) and Au NPs are prepared. In the PDMS/Au composites, the narrow extinction spectrum of Au NPs is extended over longer wavelengths by plasmonic hybridization to promote the light absorption property of the NPs. In addition, the porous structure induces strong scattering of incident light, which further enhances the absorption efficiency of the Au NPs. Consequently, the plasmon-mediated photothermal effects of Au NPs are noticeably enhanced and increased the temperature of the PDMS/Au composites to as high as 75.7 °C under artificial solar radiation, compared to 42.1 °C without the Au NPs. By applying the PDMS/Au composites to commercial TE devices, the electrical performance of the TE devices is enhanced by approximately threefold.     

Nanostructured conformal hybrid solar cells: a promising architecture towards complete charge collection and light absorption

We introduce hybrid solar cells with an architecture consisting of an electrodeposited ZnO nanorod array (NRA) coated with a conformal thin layer (<50 nm) of organic polymer-fullerene blend and a quasi-conformal Ag top contact (Thin/NR). We have compared the performance of Thin/NR cells to conventional hybrid cells in which the same NRAs are completely filled with organic blend (Thick/NR). The Thin/NR design absorbs at least as much light as Thick/NR cells, while charge extraction is significantly enhanced due to the proximity of the electrodes, resulting in a higher current density per unit volume of blend and improved power conversion efficiency. The NRAs need not be periodic or aligned and hence can be made very simply.     

Solution-processed, nanostructured hybrid solar cells with broad spectral sensitivity and stability

Hybrid organic-inorganic solar cells, as an alternative to all-organic solar cells, have received significant attention for their potential advantages in combining the solution-processability and versatility of organic materials with high charge mobility and environmental stability of inorganic semiconductors. Here we report efficient and air-stable hybrid organic-inorganic solar cells with broad spectral sensitivity based on a low-gap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and spherical CdSe nanoparticles. The solvents used for depositing the hybrid PCPDTBT:CdSe active layer were shown to strongly influence the film morphology, and subsequently the photovoltaic performance of the resulted solar cells. Appropriate post-deposition annealing of the hybrid film was also shown to improve the solar cell efficiency. The inclusion of a thin ZnO nanoparticle layer between the active layer and the metal cathode leads to a significant increase in device efficiency especially at long wavelengths, due to a combination of optical and electronic effects including more optimal light absorption in the active layer and elimination of unwanted hole leakage into the cathode. Overall, maximum power conversion efficiencies up to 3.7 ± 0.2% and spectral sensitivity extending above 800 nm were achieved in such PCPDTBT:CdSe nanosphere hybrid solar cells. Furthermore, the devices with a ZnO nanoparticle layer retained ～70% of the original efficiency after storage under ambient laboratory conditions for over 60 days without any encapsulation.     

Efficiency enhancement of graphene/silicon-pillar-array solar cells by HNO3 and PEDOT-PSS

A single-layer graphene film was grown on copper foil by chemical vapor deposition and transferred onto a silicon-pillar-array (SPA) substrate to make a Schottky junction solar cell. The SPA substrate was specifically designed to suppress reflectance and enhance light absorption. The energy conversion efficiency of the prepared graphene/SPA solar cells achieved a maximum of 2.90% with a junction area of 0.09 cm(2). HNO(3) was employed to dope the graphene in the solar cells, and the time dependence of HNO(3) treatment on the cell performance was studied. Poly(3,4-ethylenedioxythiophene) polystyrenesulfonic acid (PEDOT-PSS) was also introduced in graphene/SPA solar cells by spin coating on top of the graphene film, and its modification on the cell performance was characterized. The results show that both HNO(3) and the PEDOT-PSS film could enhance the energy conversion efficiency of graphene/SPA solar cells.     

Enhanced charge extraction for all-inorganic perovskite solar cells by graphene oxide quantum dots modified TiO2 layer

All-inorganic cesium lead bromide (CsPbBr₃) perovskite solar cells have been attracting growing interest due to superior performance stability and low cost. However, low light absorbance and large charge recombination at TiO₂/CsPbBr₃ interface or within CsPbBr₃ film still prevent further performance improvement. Herein, we report devices with high power conversion efficiency (9.16%) by introducing graphene oxide quantum dots (GOQDs) between TiO₂ and perovskite layers. The recombination of interfacial radiation can be effectively restrained due to enhanced charge transfer capability. GOQDs with C-rich active sites can involve in crystallization and fill within the CsPbBr₃ perovskite film as functional semiconductor additives. This work provides a promising strategy to optimize the crystallization process and boost charge extraction at the surface/interface optoelectronic properties of perovskites for high efficient and low-cost solar cells.     

Realization of radial p-n junction silicon nanowire solar cell based on low-temperature and shallow phosphorus doping

A radial p-n junction solar cell based on vertically free-standing silicon nanowire (SiNW) array is realized using a novel low-temperature and shallow phosphorus doping technique. The SiNW arrays with excellent light trapping property were fabricated by metal-assisted chemical etching technique. The shallow phosphorus doping process was carried out in a hot wire chemical vapor disposition chamber with a low substrate temperature of 250°C and H₂-diluted PH₃ as the doping gas. Auger electron spectroscopy and Hall effect measurements prove the formation of a shallow p-n junction with P atom surface concentration of above 10²⁰ cm⁻³ and a junction depth of less than 10 nm. A short circuit current density of 37.13 mA/cm² is achieved for the radial p-n junction SiNW solar cell, which is enhanced by 7.75% compared with the axial p-n junction SiNW solar cell. The quantum efficiency spectra show that radial transport based on the shallow phosphorus doping of SiNW array improves the carrier collection property and then enhances the blue wavelength region response. The novel shallow doping technique provides great potential in the fabrication of high-efficiency SiNW solar cells.     

3种紫细菌天然光合色素敏化DSSC光电转化性能

基于自然界光合作用机理的DSSC研究备受关注。不产氧光合细菌中的紫细菌是研究光合作用机理的良好模式生物。从3种典型紫细菌中获得了7种具有不同吸光范围、极性和结构的细菌叶绿素a（BChl a）和类胡萝卜素（Car）以及3种改性BChl a。在此基础上,较系统地比较了天然与改性BChl a、多组分与单一组分Car、BChl a色素浓度、BChl a和Car共敏对DSSC光电性能的影响,并对色素与半导体材料的相互作用进行了表征。结果表明：100 mW·cm^-2入射光强下,在不添加任何分散剂（spacer）的条件下,具有近红外吸收的天然BChl a光电转化性能较优,光电转换效率为1.26%。单一组分Car比多组分Car具有较高的光电性能,玫红品Car光电转换效率最佳。BChl a敏化TiO₂薄膜电极,吸收光谱红移,800 nm特征荧光淬灭。BChl a与Car共敏TiO₂薄膜电极,拓宽了可见光吸收光谱,短路电流和光电转换效率比BChl a提高了12%和7.3%。紫细菌天然色素廉价易得、环境友好,不仅能吸收可见光,而且能有效利用红外光,这对研制响应可见光-近红外的太阳能电池光电器件具有重要参考价值。     

基于LiCl溶液太阳能界面蒸发的连续式空气取水

太阳能吸收式空气取水利用广泛存在的太阳能和空气获取淡水,是解决淡水短缺的有效方法,然而传统技术的水分吸收和解吸收集需要分开运行,效率较低且需要人工操作。为解决该问题,提出基于吸湿盐溶液太阳能界面蒸发的连续式空气取水,一方面采用LiCl溶液吸收空气中的水分,另一方面利用太阳能界面蒸发实现溶液解吸与水蒸气冷凝收集,由于太阳能界面蒸发可以实现局部加热与解吸,吸收和解吸两个过程可以同时进行。进一步对LiCl溶液的太阳能界面蒸发与连续空气取水分别进行了试验研究,试验结果显示：质量分数为30%的LiCl溶液可以进行高效的吸收/解吸工作,在一个太阳光照强度下达到0.44 kg/(m²·h)的蒸发速率和39.3%的能量效率,并能实现连续太阳能空气取水,取水速率达到2 L/(m²·d)。     

有机-无机杂化钙钛矿太阳能电池的研究进展

有机-无机杂化钙钛矿材料不仅具有较高的光吸收能力和载流子迁移率,同时具有双极性特征以及合成方法简单等优点,目前已成为最有发展前途的太阳能电池材料,其光电转化效率在7年内从3.8%迅速提升到20%以上,并有进一步提高的空间。简单介绍了钙钛矿材料的结构与性质,综述了钙钛矿太阳能电池的研究进展,指出了目前电池发展中亟需解决的问题及未来的发展方向。     

氧化石墨烯(GO)修饰的TiO_2纳米管阵列光阳极的制备及其在染料敏化太阳能电池(DSSC)中的应用

文章采用二步阳极氧化法在纯钛片上制备了TiO2纳米管阵列,并用GO溶液修饰与其形成GO/TiO2纳米复合薄膜,修饰后的复合薄膜光电化学性能增强,组装成DSSC提高其光电转换效率,短路电流密度为13.2 mA·cm-2,光电转换效率为6.22%,相对于基于TiO2纳米管的DSSC电池分别提高了53%和30%。     

3D-carbon dots decorated black TiO2 nanotube Array@Ti foam with enhanced photothermal and photocatalytic activities

Nanostructured titanium oxide semidconductors are considered as potential materials for photothermal and photocatalytic applications. However, investigation on usage of titanium oxide nanotube array lay behind other titanium oxide nanomaterials. In order to change this uneven situation, we reported herein that carbon dots decorated black TiO₂ nanotube array@Ti foam (CDs/Black TNA@Ti) can work as highly efficient device for solar-driven water evaporation and pollutant degradation. Initially, TiO₂ nanotube array@Ti foam (TNA@Ti) was prepared through anodization of Ti foam. Through subsequent hydrogenation treatment and carbon dots decoration, CDs/Black TNA@Ti was finally achieved. It was found that CDs/Black TNA@Ti demonstrated three characters including excellent solar light absorption ability, wettability and hierarchical porous structure. For these advantages, photothermal property of TNA@Ti was stepwise improved. In solar-driven water evaporation experiment, water evaporation rate and solar thermal conversion efficiency attained 1.762 kg m⁻² h⁻¹ and 55.3% respectively for CDs/Black TNA@Ti, which are higher than previous reports on titanium oxide nanotube array. CDs/Black TNA@Ti also exhibited higher photocatalytic property than other samples without hydrogenation and/or carbon dots decoration. The CDs/Black TNA@Ti is promising for practical applications in solar-driven water evaporation and purification.     

Plasmonic antenna effects on photochemical reactions

Efficient solar energy conversion has been vigorously pursued since the 1970s, but its large-scale implementation hinges on the availability of high-efficiency modules. For maximum efficiency, it is important to absorb most of the incoming radiation, which necessitates both efficient photoexcitation and minimal electron-hole recombination. To date, researchers have primarily focused on the latter difficulty: finding a strategy to effectively separate photoinduced electrons and holes. Very few reports have been devoted to broadband sunlight absorption and photoexcitation. However, the currently available photovoltaic cells, such as amorphous silicon, and even single-crystal silicon and sensitized solar cells, cannot respond to the wide range of the solar spectrum. The photoelectric conversion characteristics of solar cells generally decrease in the infrared wavelength range. Thus, the fraction of the solar spectrum absorbed is relatively poor. In addition, the large mismatch between the diffraction limit of light and the absorption cross-section makes the probability of interactions between photons and cell materials quite low, which greatly limits photoexcitation efficiency. Therefore, there is a pressing need for research aimed at finding conditions that lead to highly efficient photoexcitation over a wide spectrum of sunlight, particularly in the visible to near-infrared wavelengths. As characterized in the emerging field of plasmonics, metallic nanostructures are endowed with optical antenna effects. These plasmonic antenna effects provide a promising platform for artificially sidestepping the diffraction limit of light and strongly enhancing absorption cross-sections. Moreover, they can efficiently excite photochemical reactions between photons and molecules close to an optical antenna through the local field enhancement. This technology has the potential to induce highly efficient photoexcitation between photons and molecules over a wide spectrum of sunlight, from visible to near-infrared wavelengths. In this Account, we describe our recent work in using metallic nanostructures to assist photochemical reactions for augmenting photoexcitation efficiency. These studies investigate the optical antenna effects of coupled plasmonic gold nanoblocks, which were fabricated with electron-beam lithography and a lift-off technique to afford high resolution and nanometric accuracy. The two-photon photoluminescence of gold and the resulting nonlinear photopolymerization on gold nanoblocks substantiate the existence of enhanced optical field domains. Local two-photon photochemical reactions due to weak incoherent light sources were identified. The optical antenna effects support the unprecedented realization of (i) direct photocarrier injection from the gold nanorods into TiO(2) and (ii) efficient and stable photocurrent generation in the absence of electron donors from visible (450 nm) to near-infrared (1300 nm) wavelengths.     

Electrophoretic deposition of nanocrystalline TiO2 films on Ti substrates for use in flexible dye-sensitized solar cells

Nanocrystalline TiO₂ films were prepared on flexible Ti-metal sheets by electrophoretic deposition followed by chemical treatment with tetra-n-butyl titanate (TBT) and sintering at 450 °C. X-ray diffraction (XRD) analysis indicates that TBT treatment led to the formation of additional anatase TiO₂, which plays an important role in improving the interconnection between TiO₂ particles, as well as the adherence of the film to the substrate, and in modifying the surface properties of the nanocrystalline particles. The effect of TBT treatment on the electron transport in the nanocrystalline films was studied by intensity-modulated photocurrent spectroscopy (IMPS). An increase in the conversion efficiency was obtained for the dye-sensitized solar cells with TBT-treated nanocrystalline TiO₂ films. The cell performance was further optimized by designing nanocrystalline TiO₂ films with a double-layer structure composed of a light-scattering layer and a transparent layer. The light-scattering effect of the double-layer nanocrystalline films was evaluated by diffuse reflectance spectra. Employing the double-layer nanocrystalline films as the photoelectrodes resulted in a significant improvement in the incident photo-to-current conversion efficiency of the corresponding cells due to enhanced solar absorption by light scattering. A high conversion efficiency of 6.33% was measured under illumination with 100 mW cm⁻² (AM 1.5) simulated sunlight.     

超薄膜吸收器在太阳能光解水制氢中的应用

太阳能光解水制氢是太阳能利用的重要途径之一。a-氧化铁是极具潜力的阳极材料, 但是a-氧化铁光生空穴的扩散长度(20 nm)远小于其光子穿透距离(波长550 nm时为120 nm), 导致电子空穴对在参与光催化反应之前发生严重的复合, 从而极大地降低太阳能利用效率。提出一种a-氧化铁/银纳米孔阵列的超薄膜双层结构, a-氧化铁的厚度仅为20 nm, 且具有很强的可见光吸收特性, 因此光生电流比相同厚度的a-氧化铁光解水电池高238%。超薄膜光学吸收的机理包括亚波长干涉共振效应和局部表面等离子激元效应, 这两种强化光学吸收的机理也可以应用于光生电荷输运能力差的半导体太阳能光伏器件。     

Simple Hierarchical Interface Design Strategy for Accelerating Solar Evaporation

Interface design is an efficient way to improve the steam generation performance of solar evaporators. Accompanied with the formation of cellulose nanofiber/polylactic acid/polyaniline (PANI) hybrid aerogel (HA) by Pickering emulsion and in situ polymerization, this paper proposes a new perspective of hierarchical interface design strategy to accelerate the water evaporation driven by solar energy. By changing the concentration and type of doped acid, the distribution gap of different PANI forms in HA can be microscopically designed. PANI nanoclusters with smaller gaps facilitate HA to achieve an improved light absorption, photothermal conversion capability and steam generation rate. Moreover, macro interface design introduces hemispherical depression structures to the HA surface through a simple mold. These recessed surfaces not only increase the light absorption by increasing the multiple reflections and refractions of light on the recesses, but also recover part of the heat radiation loss to the environment. A higher evaporation rate of 1.65 kg m⁻² h⁻¹ with a steam generation efficiency of 94.6% is achieved under the irradiation of 1 Sun (100 mw cm⁻²). Finally, HAs have strong purification ability for various raw water, and are promising in terms of their application potential in the field of energy conversion.     

Influence of nitrogen dopants on N-doped TiO2 electrodes and their applications in dye-sensitized solar cells

Three different types of nanocrystalline, N-doped TiO₂ electrodes were synthesized using several nitrogen dopants through wet methods. The obtained nanocrystalline, N-doped TiO₂ electrodes possessed different crystallite sizes, surface areas, and N-doping amounts. Characterizations were performed to reveal the nitrogen-doping processes for the wet methods using ammonia, urea, and triethylamine as the nitrogen dopants. Additionally, a high conversion efficiency of 8.32% was achieved by the dye-sensitized solar cells, based on the N-doped TiO₂ electrodes. For instance, in comparison with the commercial P25 (5.76%) and pure anatase TiO₂ electrodes (7.14%), significant improvements (44% and 17%, respectively) in the efficiencies were obtained. The findings also indicated that the ammonia nitrogen dopant was more efficient than other two nitrogen dopants. The electron transports, electron lifetimes, and charge recombination in the dye-sensitized N-doped TiO₂ solar cells also differed from those in the pure TiO₂-based dye-sensitized solar cells (DSCs). Specifically, an enhanced photocurrent of ca. 36% in N-doped DSCs resulted from the synergistic effects of the high dye uptake and the efficient electron transport. Moreover, the relationship between charge and voltage revealed that less charge was needed to get a high open-circuit voltage in the N-doping films.