Absorption of light in a single-nanowire silicon solar cell decorated with an octahedral silver nanocrystal

In recent photovoltaic research, nanomaterials have offered two new approaches for trapping light within solar cells to increase their absorption: nanostructuring the absorbing semiconductor and using metallic nanostructures to couple light into the absorbing layer. This work combines these two approaches by decorating a single-nanowire silicon solar cell with an octahedral silver nanocrystal. Wavelength-dependent photocurrent measurements and finite-difference time domain simulations show that increases in photocurrent arise at wavelengths corresponding to the nanocrystal's surface plasmon resonances, while decreases occur at wavelengths corresponding to optical resonances of the nanowire. Scanning photocurrent mapping with submicrometer spatial resolution experimentally confirms that changes in the device's photocurrent come from the silver nanocrystal. These results demonstrate that understanding the interactions between nanoscale absorbers and plasmonic nanostructures is essential to optimizing the efficiency of nanostructured solar cells.     

利用高度稳定的发光薄膜提高多晶硅太阳能电池的光伏效率（英文）

硅基太阳能电池已经主导了整个光伏市场,但是仍然面临着光电转化效率低的问题,其中部分原因是其对紫外线的利用率较低.稀土铕配合物能够将紫外光转化为可见光,有望提高硅基太阳能电池的光电转化效率.然而,这类配合物较低的稳定性限制了它们的实际应用.本文中,我们制备了一种高度稳定的EVA/Eu(ND)4-CTAC发光薄膜,将其覆盖在大尺寸的多晶硅太阳能电池表面(110 cm^2)可以使得光电转化效率从15.06%提高到15.57%.在500 h的加速老化实验中荧光性能几乎没有下降,证明了发光薄膜的超强稳定性.在如此大的有效面积上,发光薄膜使硅基太阳能电池的转换效率提高0.51%的绝对值,同时实现超高的稳定性,说明该发光膜在光伏工业上具有广阔的应用前景.     

Hybrid silicon nanocone-polymer solar cells

Recently, hybrid Si/organic solar cells have been studied for low-cost Si photovoltaic devices because the Schottky junction between the Si and organic material can be formed by solution processes at a low temperature. In this study, we demonstrate a hybrid solar cell composed of Si nanocones and conductive polymer. The optimal nanocone structure with an aspect ratio (height/diameter of a nanocone) less than two allowed for conformal polymer surface coverage via spin-coating while also providing both excellent antireflection and light trapping properties. The uniform heterojunction over the nanocones with enhanced light absorption resulted in a power conversion efficiency above 11%. Based on our simulation study, the optimal nanocone structures for a 10 μm thick Si solar cell can achieve a short-circuit current density, up to 39.1 mA/cm(2), which is very close to the theoretical limit. With very thin material and inexpensive processing, hybrid Si nanocone/polymer solar cells are promising as an economically viable alternative energy solution.     

Film adhesion in amorphous silicon solar cells

A major issue encountered during fabrication of triple junction a-Si solar cells on polyimide substrates is the adhesion of the solar cell thin films to the substrates. Here, we present our study of film adhesion in amorphous silicon solar cells made on different polyimide substrates (Kapton VN, Upilex-S and Gouldflex), and the effect of tie coats on film adhesion.     

Hydrogenated microcrystalline silicon for solar cells

We report a detailed study of the deposition, composition, structure, and photoelectric properties of low-temperature microcrystalline silicon layers produced by a novel method, which takes advantage of the activation of gas mixtures in an electron-beam plasma and the transport of the activated particles to the deposition zone at a supersonic speed. Under optimal conditions, we have reached deposition rates above 5 nm/s on substrates 150 × 150 mm in dimensions. The method under development is potentially attractive for the fabrication of thin-film solar cells through roll-to-roll processing on cheap substrates.     

Radial junction amorphous silicon solar cells on PECVD-grown silicon nanowires

Constructing radial junction hydrogenated amorphous silicon (a-Si:H) solar cells on top of silicon nanowires (SiNWs) represents a promising approach towards high performance and cost-effective thin film photovoltaics. We here develop an all-in?situ strategy to grow SiNWs, via a vapour-liquid-solid (VLS) mechanism on top of ZnO-coated glass substrate, in a plasma-enhanced chemical vapour deposition (PECVD) reactor. Controlling the distribution of indium catalyst drops allows us to tailor the as-grown SiNW arrays into suitable size and density, which in turn results in both a sufficient light trapping effect and a suitable arrangement allowing for conformal coverage of SiNWs by subsequent a-Si:H layers. We then demonstrate the fabrication of radial junction solar cells and carry on a parametric study designed to shed light on the absorption and quantum efficiency response, as functions of the intrinsic a-Si:H layer thickness and the density of SiNWs. These results lay a solid foundation for future structural optimization and performance ramp-up of the radial junction thin film a-Si:H photovoltaics.     

Nickel silicide contact for silicon solar cells

Electroless nickel metallization on textured front surface is carried out to fabricate large area (13%) efficient silicon solar cells. It is established through XPS analysis that NiSi is formed at the front grid contact on the texturized surface at relatively low temperature leading to a low value of series resistance of the solar cells.     

硅纳米线太阳能电池研究进展

硅纳米线基太阳电池相对于平面硅基太阳电池具有来源丰富低成本的特点,在未来光伏市场应用中具有一定的潜力及价值。就硅纳米线太阳能电池的工作原理,即势垒电场的形成和光生电场的产生进行了简要介绍。详细阐述了径向型和轴向型两种结构的硅纳米线太阳能电池及硅纳米线长度和微观形貌对其光电转换效率的影响。最后,对硅纳米线太阳能电池的发展进行了展望。     

Photovoltaic solar cells: Choice of materials and production methods

Photovoltaic solar cells and modules are produced for:

(i)

large scale power generation, most commonly when modules are incorporated as part of a building (building integrated photovoltaics, BIPV) but also in centralised power stations,

(ii)

supplying power to villages and towns in developing countries that are not connected to the supply grid, e.g. for lighting and water pumping systems,

(iii)

supplying power in remote locations, e.g. for communications or weather monitoring equipment,

(iv)

supplying power for satellites and space vehicles,

(v)

supplying power for consumer products, e.g. calculators, clocks, toys and night lights.

This paper reviews the choice of materials and main methods of manufacture of photovoltaic solar cells and modules that are commercially available.     

Combined power of perovskites and silicon solar cells

The photovoltaic (PV) or solar cells technology can be categorised into two main groups, the wafer‐based and thin‐film based PVs. The wafer‐based PVs include the commonly known crystalline silicon (c‐Si) and gallium arsenide (GaAs) cells. The GaAs cells exhibit higher efficiency compared to crystalline silicon (c‐Si) cells but it is the later that dominates the commercial market. Thin‐film based (2nd Generation) PVs, including cadmium telluride (CdTe), amorphous silicon (a‐Si:H) and copper‐indium‐gallium‐selenide (CIGS), generally absorb light more efficiently than wafer‐based cells and can allow the use of materials in very thin films form. CdTe PVs have proven to be highly efficient but holds only a few percentage share of the market. There is still a need for more R&D before further commercialisation. An emerging and relatively new class of thin‐film based photovoltaics (3rd Generation) technology that has the potential to overcome the current energy conversion efficiencies and performance by making use of novel materials. This class of PVs include organic photovoltaic (OPV), dye‐synthesised solar cells (DSSC), quantum‐dot (QD) and last but not least, the perovskite PV. Perovskite PVs can offer a low cost energy generation solution with the best device conversion efficiencies have shot from lower than 4% in 2009 to more than 21% in 2016. Perovskite based devices can be fabricated using vacuum thermal evaporation or by solution processing of the active layers. Although most recent perovskite solar cells with record efficiencies (>20%) are prepared via solution processing, the early breakthrough in perovskite solar cells was made with vacuum processed perovskites thin films. Vacuum thermal evaporation offers the ability and flexibility to prepare solar cell devices in various configuration. Recent developments in the field of perovskite demonstrates its compatibility with both, first and second generation PV technologies, and is therefore likely to be embraced by the conventional PV industry and make its way into utility‐scale power generation.     

用于HIT太阳能电池的本征非晶硅薄膜

带本征薄层的异质结（HIT）太阳能电池要求本征非晶硅薄膜具有生长速率低，暗电导大，光学带隙宽的特点。采用等离子增强化学气相沉积（PECVD）制备符合HIT太阳能电池要求的本征非晶硅薄膜，并通过分析薄膜的透射光谱，采用Tauc法计算了薄膜的光学带隙，为约1．87eV，衬底温度为180℃，放电功率为80W时获得的薄膜性能最佳。     

Vacuum-deposited polycrystalline silicon solar cells on foreign substrates

The problem of fabricating low cost solar cells on foreign substrates has been addressed through the use of vacuum-deposited polycrystalline silicon films. The experimental cells consisted of the following layers on an Al₂O₃ substrate: TiB₂ bottom electrode/p-type polycrystalline silicon film/n-type silicon region/Ti---Ag electrode. The formation and properties of each layer are described. Interfacial reactions and purity were examined by secondary ion mass spectrometry, X-ray diffraction and scanning electron microscopy. A reactionbettween silicon and TiB₂ resulting in large silicon crystallite growth has been identified. The n-type region was formed by standard phosphorus diffusion techniques. Typical photovoltaic responses without an antireflection coating were V_oc = 0.28 V, J_sc = 18 mA cm^-2, an efficiency of 2.7% and a fill factor of 0.55. The factors limiting the cell efficiency were primarily the grain size and the purity of the p-type silicon layer.     

Nanoimprint lithography for high-efficiency thin-film silicon solar cells

We demonstrate high-efficiency thin-film silicon solar cells with transparent nanotextured front electrodes fabricated via ultraviolet nanoimprint lithography on glass substrates. By replicating the morphology of state-of-the-art nanotextured zinc oxide front electrodes known for their exceptional light trapping properties, conversion efficiencies of up to 12.0% are achieved for micromorph tandem junction cells. Excellent light incoupling results in a remarkable summed short-circuit current density of 25.9 mA/cm(2) for amorphous top cell and microcrystalline bottom cell thicknesses of only 250 and 1100 nm, respectively. As efforts to maximize light harvesting continue, our study validates nanoimprinting as a versatile tool to investigate nanophotonic effects of a large variety of nanostructures directly on device performance.     

Silicon quantum dot/crystalline silicon solar cells

Silicon (Si) quantum dot (QD) materials have been proposed for 'all-silicon' tandem solar cells. In this study, solar cells consisting of phosphorus-doped Si QDs in a SiO(2) matrix deposited on p-type crystalline Si substrates (c-Si) were fabricated. The Si QDs were formed by alternate deposition of SiO(2) and silicon-rich SiO(x) with magnetron co-sputtering, followed by high-temperature annealing. Current tunnelling through the QD layer was observed from the solar cells with a dot spacing of 2?nm or less. To get the required current densities through the devices, the dot spacing in the SiO(2) matrix had to be 2?nm or less. The open-circuit voltage was found to increase proportionally with reductions in QD size, which may relate to a bandgap widening effect in Si QDs or an improved heterojunction field allowing a greater split of the Fermi levels in the Si substrate. Successful fabrication of (n-type) Si QD/(p-type) c-Si photovoltaic devices is an encouraging step towards the realization of all-silicon tandem solar cells based on Si QD materials.     

Texturization of multicrystalline silicon by wet chemical etching for silicon solar cells

Two kinds of surface texturization of mc-Si obtained by wet chemical etching are investigated in view of implementation in the solar cell processing. The first one was the acid texturization of saw damage on the surface of multicrystalline silicon (mc-Si). The second one was macro-porous texturization prepared by double-step chemical etching after KOH saw damage layer was previously removed.Both methods of texturization are realized by chemical etching in HF-HNO₃-H₂O with different additives. Macro-porous texturization allows to obtain effective reflectivity (R_eff) in the range 9–20% from bare mc-Si. This R_eff value depends on the time of second step etching that causes porous structure modification. The internal quantum efficiency (IQE) of cells with this kind of texturization has possibility to reach better conversion efficiency than the standard mc-Si solar cells. However, low shunt resistance depends on morphology of porous layer and it is the main factor which can reduce open circuit voltage and conversion efficiency of cells.The effective reflectivity is about 17% for acid texturized mc-Si wafer. The investigation of surface morphology by scanning electron microscopy (SEM) revealed that the dislocations are appearing during chemical etching and they can reduce open circuit voltage. The density of the dislocations can be reduced by controlling depth of etching and optimisation of acid solution.     

Photovoltaic contribution of photo-generated excitons in acceptor material of organic solar cells

Contribution of exciton generation in acceptor material to the photovoltaic performance of three bulk-heterojunction organic solar cells (BHJ OSCs), PTB7:PC₇₁BM, P3HT:ICBA and P3HT:PC₆₁BM are studied. Singlet and triplet rates of absorption and dissociation and diffusion lengths are calculated and compared with those when excitons are generated in the donor of these BHJ OSCs. It is found that the rates of absorption and dissociation and diffusion lengths are comparable whether excitons are generated in donor or acceptor of these BHJ OSCs. Therefore, it is proposed that the contribution of exciton generation in acceptor may not be negligible.