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We show that SiO-based intermediate reflectors ͑SOIRs͒ can be fabricated in the same reactor and with the same process gases as used for thin-film silicon solar cells. By varying input gas ratios, SOIR layers with a wide range of optical and electrical properties are obtained. The influence of the SOIR thickness in the micromorph cell is studied and current gain and losses are discussed. Initial micromorph cell efficiency of 12.2% ͑V oc = 1.40 V, fill factor= 71.9%, and J sc = 12.1 mA/ cm 2 ͒ is achieved with top cell, SOIR, and bottom cell thicknesses of 270, 95, and 1800 nm, respectively.A micromorph tandem solar cell consists of a high-gap amorphous ͑a-Si: H͒ top cell and a low-gap microcrystalline silicon ͑ c-Si: H͒ bottom cell stacked on top of each other. The thickness of the a-Si: H cell has to be kept reasonably thin to minimize the impact of light-induced degradation, 1 and its current, therefore, generally limits the current of the tandem device. To overcome this issue, an intermediate reflecting layer ͑IRL͒ can be introduced between the two cells to increase the current of the top cell. 2 For an intermediate layer to act as a reflector, its refractive index n must be lower ͑typically n IRL Ϸ 2͒ than that of silicon ͑n Si = 3.8 at 600 nm͒ such as to produce a refractive index step that causes the reflection of light at the material interface. The layer which serves as IRL is required to be sufficiently conductive to avoid blocking current and as transparent as possible to minimize the current losses due to absorption of light outside the active layers. In the first attempts to realize this intermediate reflector, zinc oxide ͑ZnO͒ has been used. [2][3][4] In a recent study, the top-cell current could be increased by 2.8 mA/ cm 2 , using a 110-nm-thick ZnO IRL with a 180-nm-thick top cell. 3 When considering industrialization, there are, however, two main drawbacks of ZnO-based IRL: the need for an additional ex situ deposition step and an additional laser scribe for monolithic series interconnection to avoid lateral shunting of solar module segments. 5 Another group reported in situ fabrication of a different IRL but without specifying the material used. 6 In this paper, we propose the preparation of an IRL based on a "doped silicon oxide" material fabricated by plasma enhanced chemical vapor deposition ͑PECVD͒ in the same reactor as the solar cells. We demonstrate that it is possible to produce such a SiObased intermediate reflector ͑SOIR͒, with a refractive index close to 2 and electrical properties suitable for incorporation into micromorph devices.The SiO-based layers are deposited by very-high frequency PECVD at 110 MHz, 200°C, and with a power density of 0.01-0.1 W / cm 2 . Optical and electrical characterizations are performed on ϳ100-nm-thick layers deposited on glass. Optical reflectance and transmittance are measured with a Perkin-Elmer photospectrometer, type lambda 900, within a spectral range from 320 to 2000 nm. The refractive index n and the absorption coefficient ␣ are estimated by fitti...

The deposition of thin-film silicon solar cells on highly textured substrates results in improved light trapping in the cell. However, the growth of silicon layers on rough substrates can often lead to undesired current drains, degrading performance and reliability of the cells. We show that the use of a silicon oxide interlayer between the active area and the back contact of the cell permits in such cases to improve the electrical properties. Relative increases of up to 7.5% of fill factor and of 6.8% of conversion efficiency are shown for amorphous silicon cells deposited on highly textured substrates, together with improved yield and low-illumination performance.

The micromorph solar cell concept consists of an optical and electrical series connection of a high-gap a-Si:H top cell and a low-gap µc-Si:H bottom cell. To minimize light-induced degradation, the thickness of the a-Si:H absorber should not exceed 300 nm. This constraint considerably limits the short-circuit current density (J sc ) on the top cell and, hence, the efficiency of the whole device. Therefore an intermediate reflecting layer (IRL) between the individual cells must be introduced to increase the current in the a-Si:H absorber [1][2][3][4].In this letter, we first analyze the light scattering properties of nano-textured transparent conductive oxide (TCO) layers used as front electrodes for micromorph cells deposited in the superstrate configuration (p-i-n). Photocurrents in individual state-of-the-art cells with a Si oxide based IRL (SOIR) are then compared for front TCOs with different surface morphologies and the observed differences are related to the optical characteristics of these TCOs.The three types of TCO (type-A, -B and -C) used in this study are as-grown surface textured ZnO films with two different doping levels obtained by low-pressure chemical vapour deposition (LPCVD) on Schott AF45 glass substrates. The thickness of the resulting layers is adjusted to obtain a sheet resistance below 10 Ω/sq. The root mean square value of their surface roughness (σ rms ) and the correlation length ξ of the textured surface are determined by atomic force microscopy. These characteristics, summarized in Table 1, depend on the thickness of the layers and on the duration of a plasma post-treatment [5] applied to their surface. Note that the type-B ZnO (without posttreatment), whose sharp V-shape structures prevent good electrical properties of the device [5], is presented only for the sake of light scattering comparisons. The low doping level used for deposition of the thick large-grain ZnO layers (type-B and -C) provides high transparency in the near infrared (NIR) spectral range because of reduced free carrier absorption (FCA) [6]. The diffuse transmittance in-air of the different TCOs, when light is normally incident to the glass side, is investigated by two methods. First, the haze factor for transmitted light H T = T dif /T tot is calculated from total and diffuse optical transmittance (T tot and T dif ) measurements carried out with a photo-spectrometer equipped with an integration-sphere. Second, the intensity per unit of solid angle scattered at an angle θ with respect to the direction of an incident laser beam (633 nm) is deIn the effort to increase the stable efficiency of thin film silicon micromorph solar cells, a silicon oxide based intermediate reflector (SOIR) layer is deposited in situ between the component cells of the tandem device. The effectiveness of the SOIR layer in increasing the photo-carrier generation in the a-Si : H top absorber is compared for p -i -n devices deposited on different rough, highly transparent, front ZnO layers. High haze and low doping level for the front ZnO stron...

We propose the use of transparent replicated random nanostructures fabricated via nanoimprinting on glass as next-generation superstrates for thin film silicon solar cells. We validate our approach by demonstrating short-circuit current densities for p-i-n hydrogenated microcrystalline silicon solar cells as high as for state-of-the-art nanotextured ZnO front electrodes. Our methodology opens exciting possibilities to integrate a large variety of nanostructures into p-i-n solar cells and allows to systematically investigate the influence of interface morphology on the optical and electronic properties of the device in order to further improve device performance.