Researchers double efficiency of black silicon solar cells

By modifying the shape of the laser pulse uses to irradiate the silicon, the researchers were able to create cells that can produce more electricity from the infrared spectrum, something normal solar cells can't do. "In normal silicon, infrared light does not have enough energy to excite the electrons into the conduction band and convert them into electricity, but the sulfur incorporated in black silicon forms a kind of intermediate level," explained Dr Stefan Kontermann form the Fraunhofer Institute for Telecommunications. "You can compare this to climbing a wall: the first time you fail because the wall is too high, but the second time you succeed in two steps by using an intermediate level. However, in sulfur this intermediate level not only enables electrons to climb the 'wall', it also works in reverse, enabling electrons from the conduction band to jump back via this intermediate level, which causes electricity to be lost once again." By modifying the laser pulse that drives the sulfur atoms into the atomic lattice, the researchers were able to change the positions that these atoms adopted in the lattice and change the height of their 'levels', in other words their energy level. "We used the laser pulses to alter the embedded sulfur in order to maximise the number of electrons that can climb up while minimising the number that can go back down," Dr Kontermann continued. The Fraunhofer team is now working on using different shapes of laser pulses and analysing how this changes the energy level of the sulfur. In the future, the researchers hope that a system of algorithms will automatically identify how the laser pulse should be modified in order to achieve optimum efficiency.