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Why Not the Sun? Advantages of and Problems with Solar Energy
(Released December 2008)

  by Ethan Goffman  


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Choose a Category Silicon Photovoltaics   Thin Film
  Solar Thermal   Economics
  1. Defect states on the surfaces of a P-type c-Si wafer and how they control the performance of a double heterojunction solar cell

    Antara Datta, J. Damon-Lacoste, P. Roca i. Cabarrocas and P. Chatterjee.

    Solar Energy Materials and Solar Cells, Vol. 92, No. 11, Nov. 2008, pp. 1500-1507.

    'Heterojunction with intrinsic thin layer'solar cells combine the high efficiency of crystalline silicon (c-Si) cells, with the low cost of amorphous silicon technology. Here we use detailed numerical modeling and experiments to understand the influence, on the solar cell output parameters, of defects on the front and rear surfaces of the P-type c-Si wafer. Modeling indicates that the defects on the front surface of c-Si reduce the open-circuit voltage and fill factor, while those on the rear surface degrade mainly the short-circuit current density and fill factor, but only when their density exceeds 1012 cm-2.

  2. Effect of hydrogen dilution on intrinsic a-Si:H layer between emitter and Si wafer in silicon heterojunction solar cell

    Sang-Kyun Kim, Jeong Chul Lee, Seong-Ju Park, Youn-Joong Kim and Kyung Hoon Yoon.

    Solar Energy Materials and Solar Cells, Vol. 92, No. 3, Mar. 2008, pp. 298-301.

    In silicon heterojunction solar cells, a thin intrinsic amorphous-silicon (a-Si:H) buffer layer between a doped emitter and a c-Si wafer is essential to minimize carrier recombination. This study examines the effect of H2 dilution on the properties of the intrinsic a-Si:H layers deposited on Si wafers by plasma-enhanced chemical vapor deposition. A H2/SiH4 ratio of 24 led to improvements in the quality of intrinsic a-Si:H films and in the performance of passivation compared to a-Si:H film without H2 dilution. A high H2-dilution ratio, however, degraded the passivation of the a-Si:H film. The Si heterojunction solar cells with an optimal intrinsic a-Si:H layer showed an efficiency of 12.3%.

  3. Screen-print selective diffusions for high-efficiency industrial silicon solar cells

    Matthew Edwards, Jonathan Bocking, Jeffrey E. Cotter and Neil Bennett.

    Progress in Photovoltaics, Vol. 16, No. 1, Jan. 2008, pp. 31-45.

    Screen-print diffusion pastes present an industrially applicable alternative to conventional techniques of dopant deposition. Several commercially available screen-print dopant pastes are assessed for their suitability in forming heavy selective diffusions for use under metal contacts in silicon solar cells. Pastes are assessed in terms of their ease of application, their ability to form heavy diffusions with low sheet resistances, and their ability to maintain high post-diffusion wafer lifetimes. Potential for the use of dopant pastes in high-efficiency solar cell devices is investigated using photoconductance (PC) measurements and photoluminescence (PL) images. It is found that under certain conditions, screen-print dopant pastes, particularly phosphorus paste, have potential to form effective selective diffusions without significantly compromising performance in high-efficiency solar cells.

  4. Stability of microcrystalline silicon solar cells with HWCVD buffer layer

    Y. Wang, X. Geng, H. Stiebig and F. Finger.

    Thin Solid Films, Vol. 516, No. 5, 15 Jan 2008, pp. 733-735.

    Microcrystalline silicon solar cells deposited by VHF-PECVD with or without HWCVD grown p/i interface buffer layer were investigated. We studied long-term stability under storage in ambient atmosphere and performed light soaking experiments. Cells with i-layers covering a wide range of crystalline volume fractions were studied. All cells were stable or degraded slightly after storage for 2 years in air, regardless of crystalline volume fraction or presence of p/i buffer interface. Upon light soaking all cells show efficiency degradation to more or less extent depending on crystal volume fraction of the i-layer and the presence of the buffer layer: the solar cell with high crystal volume fraction are nearly stable, cells with high amorphous volume fraction degrade by up to 20%. The solar cell with HWCVD buffer layer shows better stability in the high efficiency range of relative efficiency degradation typically less than 10% after 1000 h AM 1.5 light soaking. The efficiency degradation is mainly caused by Voc and FF deterioration while Jsc is almost stable.

  5. Theory and experiments on the back side reflectance of silicon wafer solar cells

    Daniel Kray, Martin Hermle and Stefan W. Glunz.

    Progress in Photovoltaics, Vol. 16, No. 1, Jan. 2008, pp. 1-15.

    New passivation layers for the back side of silicon solar cells have to show high performance in terms of electrical passivation as well as high internal reflectivity. This optical performance is often shown as values for the back side reflectance Rb which describes the rear internal reflection. In this paper, we investigate in detail the meaning of this single-value parameter, its correct determination and the use in one-dimensional simulations with PC1D. The free-carrier-absorption (FCA) as non-carrier-generating absorption channel is analyzed for solar cells with varying thickness. We apply the optical analysis to samples with different thickness, silicon oxide layer thickness, rear side topography as well as passivation layers (SiO2, SiNx, SiC and stack systems). Additionally, the optical influence of the laser-fired contacts (LFC) process is experimentally investigated. Finally, we show that with correct parameters, the one-dimensional simulation of very thin silicon solar cells can successfully be performed.