The efficiency of silicon solar cells has a large influence on the cost of most photovoltaics panels. Here, researchers from Kaneka present a silicon heterojunction with interdigitated back contacts reaching an efficiency of 26.3% and provide a detailed loss analysis to guide further developments.

Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26

Low cost photovoltaic modules based on dye sensitized nanocrystalline titanium dioxide and carbon powder

Silicon nanowire-based solar cells on metal foil are described. The key benefits of such devices are discussed, followed by optical reflectance, current-voltage, and external quantum efficiency data for a cell design employing a thin amorphous silicon layer deposited on the nanowire array to form the p-n junction. A promising current density of ∼1.6mA∕cm2 for 1.8cm2 cells was obtained, and a broad external quantum efficiency was measured with a maximum value of ∼12% at 690nm. The optical reflectance of the silicon nanowire solar cells is reduced by one to two orders of magnitude compared to planar cells.

Silicon nanowire solar cells

With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

/pdf/high-efficiency-crystalline-silicon-solar-cells-status-and-47y1w8zg6w.pdf

High-efficiency crystalline silicon solar cells: status and perspectives

The high natural abundance of silicon, together with its excellent reliability and good efficiency in solar cells, suggest its continued use in production of solar energy, on massive scales, for the foreseeable future. Although organics, nanocrystals, nanowires and other new materials hold significant promise, many opportunities continue to exist for research into unconventional means of exploiting silicon in advanced photovoltaic systems. Here, we describe modules that use large-scale arrays of silicon solar microcells created from bulk wafers and integrated in diverse spatial layouts on foreign substrates by transfer printing. The resulting devices can offer useful features, including high degrees of mechanical flexibility, user-definable transparency and ultrathin-form-factor microconcentrator designs. Detailed studies of the processes for creating and manipulating such microcells, together with theoretical and experimental investigations of the electrical, mechanical and optical characteristics of several types of module that incorporate them, illuminate the key aspects.

Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs

Our unique, high-efficiency c-Si solar cell, named the HIT cell, has shown considerable potential to improve junction properties and surface passivation since it was first developed. The improved properties in efficiency and temperature dependence compared to conventional p – n diffused c-Si solar cells are featured in HIT power 21TM solar cell modules and other applications which are now on the market. In the area of research, further improvement in the junction properties of the a-Si/c-Si heterojunction has been examined, and the highest efficiency to date of 20.1% has recently been achieved for a cell size of 101 cm2. The high open circuit voltage exceeding 700 mV, due to the excellent surface passivation of the HIT structure, is responsible for this efficiency. In this paper, recent progress in HIT cells by Sanyo will be introduced. Copyright © 2000 John Wiley & Sons, Ltd.

HITTM cells—high-efficiency crystalline Si cells with novel structure

PURPOSE:To improve the electric energy conversion efficiency of the converter by a structure wherein a light transmitting layer containing fluorescent material, the fluorescent local maximum wave length of which lies within the effective sensitivity spectrum of solar cells, is adhered on the light receiving surface of a heat collecting plate and solar cells are provided at the sides of said light transmitting layer CONSTITUTION:The light transmitting layer 3 containing fluorescent material, the fluorescent local maximum wave length of which lies within the effective sensitivity spectrum of the solar cells 5, is adhered on the light receiving surface of the heat collecting plate 2 and as well as the solar cells 5 are provided at the sides of said light transmitting layer 3 in the solar energy converter comprising heat transfer medium conduits 6, a heat transfer medium pipe 1, the heat collecting plate 2, which is connected with the pipe 1 to be conductive of heat, and the solar cells 5 Concretely, the light, the wave length of which the sensitivity of the solar cells 5 is low, in the solar spectra is absorbed by the fluorescent material in the light transmitting layer 3 and converted into the light, to the wave length of which the solar cells 5 are strikingly sensitive, and said fluorescent light falls on the light receiving surface of the cells 5, resulting in converting said incident light into electric energy with high efficiency As a matter of course, the light having the wave lengths of about 055-06mum, which is originally contained in the sun light itself, is efficiently collected by the cells 5

Solar energy converter

A new method to determine the optical absorption coefficient (α) of thin films is presented. α of hydrogenated amorphous silicon (a-Si:H) based alloys can be accurately determined from transmittance (T) and reflectance (R) by using T/(1-R), which almost completely eliminates disturbance from the optical interference effect. The method is applicable to any thin films, as long as the film is a single layer. Based on the interference-free α, various methods to determine the optical gap (EOPT) of a-Si:H, a-SiC:H, and a-SiGe:H films are discussed. The (nαhν)1/3 plot and the (αhν)1/3 plot are most suitable for characterizing these films. The well-known (αhν)1/2 plot is less suited for detailed discussion of the EOPT than the cube root plot, because the plot includes a large ambiguity in the EOPT. The effect of the optical interference effect on the determination of the EOPT is also discussed.

https://iopscience.iop.org/article/10.1143/JJAP.30.1008/pdf

Interference-Free Determination of the Optical Absorption Coefficient and the Optical Gap of Amorphous Silicon Thin Films

The influence of the Si-H2 bond on light-induced degradation and the thermal recovery of a-Si films and a-Si solar cells were studied. The influence of the Si-H2 bond on light-induced degradation depends on the impurity content in a-Si films, and light-induced degradation can be reduced by decreasing the Si-H2 bond density in a-Si films with impurity content of 1018 cm-3. The activation energy of the thermal recovery process was about 1.0 eV, and it did not depend on the Si-H2 bond density. However, an irreversible phenomenon was observed in film properties and solar cell characteristics with high Si-H2 bond density. It is thought that the structural flexibility of the Si-H2 bond is related to this irreversible phenomenon.

https://iopscience.iop.org/article/10.1143/JJAP.28.1762/pdf

The Influence of the Si-H2 Bond on the Light-Induced Effect in a-Si Films and a-Si Solar Cells

A laser patterning method was investigated as a fabrication method for integrated-type amorphous-silicon (a-Si) solar cell submodules. A three-dimensional thermal analysis of a multilayer structure was performed to determine the selective scribing conditions for each layer of an a-Si solar cell. The optimum laser power densities calculated from a three-dimensional thermal analysis were confirmed by the experiments. It was found that not only transparent conductive oxide and a-Si films, but also the metal electrodes of the integrated-type a-Si solar cell submodule were selectively scribed. The total output power of an a-Si solar cell submodule patterned by optimum laser-power densities was 9% higher than that achieved by a conventional patterning method.

Noboru Nakamura

Papers

HITTM cells—high-efficiency crystalline Si cells with novel structure

Solar energy converter

Interference-Free Determination of the Optical Absorption Coefficient and the Optical Gap of Amorphous Silicon Thin Films

The Influence of the Si-H2 Bond on the Light-Induced Effect in a-Si Films and a-Si Solar Cells

Laser Patterning Method for Integrated Type a-Si Solar Cell Submodules