With 79% transparency, Schottky junction invisible solar cell unveiled

Using indium tin oxide (ITO) and tungsten disulphide (WS2) as substrates, Japanese scientists have developed a near-invisible solar cell. the ITO and WS2 act as a transparent electrode and a photoactive layer respectively.

This photovoltaic device is also known as a Schottky junction solar cell, according to a recently published report. This is an interface between a metal and a semiconductor that further provides the necessary band for charge separation. The power conversion efficiency of this solar cell is 1000 times higher than that of a reference device using ordinary ITO electrodes.

The scientists further note that the cell has a transparency of 79% and add: "We have also investigated the large-scale manufacture of solar cells. The results show that even if the device area is increased, a simple size scaling using large WS2 crystals and parallel-length electrodes does not improve the total power of the whole device."

The article titled "Fabrication of near-invisible solar cells with a single layer of WS2" refers to the new cell technology. The scientists also said that the findings could help in the study of near-invisible solar cells using transition metal dichloride, from the basic to the real industrial stage.

The report quotes the scientists as saying, "Once the generated carriers travel to the opposite electrodes, electricity generation can be achieved." The difference in the work function between one of the electrodes and the semiconductor separates the photogenerated electron-hole pairs.

WS2 is a member of the family of transition metal dichloride materials. In the visible range, WS2 has a suitable band gap and the highest absorption coefficient per unit thickness, making it ideal for near-invisible solar cells. itO-WS2 junctions are achieved by sputtering ITO on a quartz substrate, and WS2 monolayers are grown separately by chemical vapour deposition.

The idea of near-invisible solar cells is attractive due to the many new applications that can be created for solar photovoltaics, especially on buildings. The solar energy can go beyond the roof and also into the sides, especially on the south side where there is no shade whatsoever.

PV Tech understands that the solar company NewEnergyTechnologiesInc. has previously developed a transparent solar cell and claims to mass produce this "invisible" solar cell because it is so transparent that even if it is installed on the surface of a window, it does not affect the light transmission of the glass. The glass will not be affected by the light transmission.

Last year, South Korean researchers also claimed to have found an effective and inexpensive way to convert solar cells from opaque to transparent. Existing transparent solar cells tend to have a reddish tinge and are less efficient, but by punching holes of about 100μm in diameter (the size of a hair) into the crystalline silicon wafer, light can be allowed to pass through without having to colour the cell. These holes are strategically distributed on the wafer so that the human eye cannot "see" it. The research was published in the journal Joule.

In recent decades, solar cells have become cheaper, more efficient and more environmentally friendly. However, current applications of solar modules are limited to rooftops and remote solar power plants, and it is worth thinking about how they can be better used in people's lives.

What if, for example, the next generation of solar modules could be integrated into windows, buildings and even mobile phone screens?