Silicon solar cells are described which operate at energy conversion efficiencies independently measured at 18.7 percent under standard terrestrial test conditions (AM1.5, 100 mW/cm2, 28°C). These are apparently the most efficient silicon cells fabricated to date. The high-efficiency results from a combination of high open-circuit voltage due to the careful attention paid to the passivation of the top surface of the cell; high fill factor due to the high open-circuit voltage and low parasitic resistance losses; and high short-circuit current density due to the use of shallow diffusions, a low grid coverage, and an optimized double layer antireflection coating.

High-efficiency silicon solar cells

The global photovoltaic (PV) market is dominated by crystalline silicon (c-Si) based technologies with heavily doped, directly metallized contacts. Recombination of photo-generated electrons and holes at the contact regions is increasingly constraining the power conversion efficiencies of these devices as other performance-limiting energy losses are overcome. To move forward, c-Si PV technologies must implement alternative contacting approaches. Passivating contacts, which incorporate thin films within the contact structure that simultaneously supress recombination and promote charge-carrier selectivity, are a promising next step for the mainstream c-Si PV industry. In this work, we review the fundamental physical processes governing contact formation in c-Si. In doing so we identify the role passivating contacts play in increasing c-Si solar cell efficiencies beyond the limitations imposed by heavy doping and direct metallization. Strategies towards the implementation of passivating contacts in industrial environments are discussed. The development of passivating contacts holds great potential for enhancing the power conversion efficiency of silicon photovoltaics. Here, De Wolf et al. review recent advances in material design and device architecture, and discuss technical challenges to industrial fabrication.

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Passivating contacts for crystalline silicon solar cells

An object is to provide a method for manufacturing a semiconductor device, in which the number of photolithography steps can be reduced, the manufacturing process can be simplified, and manufacturing can be performed with high yield at low cost A method for manufacturing a semiconductor device includes the following steps: forming a semiconductor film; irradiating a laser beam by passing the laser beam through a photomask including a shield for shielding the laser beam; subliming a region which has been irradiated with the laser beam through a region in which the shield is not formed in the photomask in the semiconductor film; forming an island-shaped semiconductor film in such a way that a region which is not irradiated with the laser beam is not sublimed because it is a region in which the shield is formed in the photomask; forming a first electrode which is one of a source electrode and a drain electrode and a second electrode which is the other one of the source electrode and the drain electrode; forming a gate insulating film; and forming a gate electrode over the gate insulating film

Method for Manufacturing Semiconductor Device

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 SiO2 matrix deposited on p-type crystalline Si substrates (c-Si) were fabricated. The Si QDs were formed by alternate deposition of SiO2 and silicon-rich SiOx 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 SiO2 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.

https://iopscience.iop.org/article/10.1088/0957-4484/19/24/245201/pdf

Silicon quantum dot/crystalline silicon solar cells.

A high efficiency thin film silicon solar cell and module

A new type of amorphous silicon (a-Si) solar cell stacked with polycrystalline silicon (poly-c-Si) has been developed. The conversion efficiency more than 12% has been obtained with a cell structure of ITO//n-i-p a-Si//n a-Si/p poly c-Si//Al. A series of technical data on the cell fabrication and resulting photovoltaic characteristics are presented.

https://iopscience.iop.org/article/10.1143/JJAP.22.L605/pdf

Amorphous Si/Polycrystalline Si Stacked Solar Cell Having More Than 12% Conversion Efficiency

PURPOSE:To improve conversion efficiency, and to manufacture the photovoltage cell at low cost by joining a unit cell consisting of an amorphous semiconductor with the amorphous semiconductor hetero-junctioned with the single crystal or polycrystalline crystal system semiconductor. CONSTITUTION:K+2C (K=1 or 2 and C is zero or an integer) P type polycrystalline semiconductors 11p and at least each one of P type, I type and N type 2-K+3A (A is an integer) amorphous or crystallite semiconductors 20n are hetero-junctioned HJ, thus forming the unit cell. P type amorphous silicon (P-aSi) 21p, I type amorphous silicon (I-aSi) 21i and N type amorphous silicon (N-aSi) or N type crystallite silicon (N-thetaC.Si) 21n constitute an amorphous unit cell P-I-N joined. A transparent conductive film 10 as an electrode is formed on the semiconductor 21n. The unit cell of the semiconductor 20n absorbs light on the short wavelength side in incident light, and the semiconductor 11p absorbs light on the long wavelength side, thus effectively utilizing light extending over a wide range by the single photovoltaic cell.

Hetero-junction photovoltaic cell of crystal system semiconductor and amorphous semiconductor

PURPOSE:To contrive to reduce the manufacturing cost by forming a P-N junction by depositing an amorphous semiconductor on a crystalline semiconductor in a low temperature process. CONSTITUTION:An electrode 1 is formed by evaporating aluminum on the back surface of a P type polycrystalline Si wafer 2, an N type thin film semiconductor 3 and a clear conductive film 4 made of the compound of Ind oxide with Sn oxide are formed on the wafer 2 by glow discharge decomposition, and then a comb electrode 5 is formed on said film 4. Said wafer 2 and said semiconductor 3 are put in hetero junction and thus constitute the unit cell of the solar battery. Since the P-N junction can be formed in the low temperature process such as a glow discharge decomposition method by changing the N type semiconductor 3 into a thin film microcrystalline Si, the reduction of the manufacturing cost can be contrived.

Hetero junction solar battery and manufacture thereof

Spectroscopic analysis of the laser beam induced current (LBIC) has been carried out as a powerful tool for characterizations of spacial homogeneity and surface and junction interfaces in amorphous silicon (a-Si) solar cells. We have found the photocurrent inhomogeneity of a-Si solar cells and analyzed the origins of the fluctuation using the spectroscopic LBIC measurement. There are three kinds of fluctuation patterns, i.e., spikes based on the dust and scratch of the film, aligned sinusoidal fluctuation with short period upon the glass substrate thickness inhomogeneity, and relatively long period oscillation based on the a-Si junction interface situation. It has also been revealed that a spectroscopic technique varing the wavelength of probe light makes it possible to know the in-depth profile of opto-electronic properties as well as optical properties of semiconductor devices.

Spectroscopic Laser Scanning Analysis of Photo-Induced Current on a-Si Solar Cells

We have fabricated a junction of a Si waveguide to plasmonic waveguide supporting the second plasmon mode as a first step to realize high density integrated optical circuit. We successfully excited the second plasmonic mode by using Si waveguide and evaluated that the coupling efficiency is about 7.5%.

Koji Okuda

Papers

Amorphous Si/Polycrystalline Si Stacked Solar Cell Having More Than 12% Conversion Efficiency

Hetero-junction photovoltaic cell of crystal system semiconductor and amorphous semiconductor

Hetero junction solar battery and manufacture thereof

Spectroscopic Laser Scanning Analysis of Photo-Induced Current on a-Si Solar Cells

Gap plasmon excitation into plasmonic waveguide using Si waveguide