Could solar cells in your smartphone’s screen power the device?
Transparent solar cells offer a range of possibilities to reduce our dependence on non-sustainable energy sources – from on-site power generation in densely populated urban areas to the ability to power an electronic device via its screen. Recent improvements have increased the efficiency and transparency of organic solar cells, making them a more viable option for companies looking to reduce their environmental impact.
Organic solar 
cells are photovoltaic devices made from conductive polymers. They are lightweight, flexible and inexpensive to produce in high volumes. They are less efficient at converting direct solar energy into electricity than traditional crystalline silicon solar panels, but they operate well in diffuse and low-light settings. They can also fabricated as semi-transparent devices, giving them a broad new range of applications.
In order to produce semi-transparency in the cells, the back metal electrode is reduced to only few nanometers thick. Compared to equivalent opaque devices, transparent solar cells are less efficient because the reduction in electrode thickness decreases the cell’s reflectivity and photon-harvesting capability.
Recently, a group of researchers at the Institute of Photonic Sciences (ICFO) and the Polytechnic University of Catalonia (UPC) have improved the effectiveness of semi-transparent solar cells by using a non-periodic photonic crystal to capture near-infrared and near-ultraviolet photons. Their cells achieved 30% visible light transmission and up to 5.6% power conversion efficiency. The overall light harvesting capacity of the device was 77% of its opaque counterpart – a considerable improvement over the 61% effectiveness that was previously achievable. The colour of the solar cells can also be changed easily without significantly impacting performance.
The results are promising for improving the viability of building-integrated photovoltaic (BIPV) technology applications. While more work is necessary to achieve the “extremely high transparencies and efficiencies needed to power up devices such as displays, tablets, smart phones, etc.”, said team leader Jordi Martorell, “applications for this type of technology in BIPV are just a few steps away.” Given the energy production potential for building-integrated photovoltaic technologies in urban areas, transparent solar cells have a bright future ahead.
Image: Nature Photonics
