Scientists at the National Institute for Materials Science (NIMS) announced the improvement of power conversion efficiency (PCE) of perovskite solar cells to over 16% while employing cells that were greater than 1 cm2. The high efficiency cells also passed the durability test (exposure to AM 1.5G 100 mW/cm2 sunlight for 1,000 hours), which is considered to be a basic criterion for practical use. These achievements were made by replacing the conventional organic materials with inorganic materials as the electron and hole extraction layers of the solar cells.
The researchers replaced the conventional organic materials with robust inorganic materials for use in electron and hole extraction layers. Since these layers have high electrical resistance, it was necessary to reduce the thickness of the layers to several nanometers. However, as the area of these thin layers increases, the occurrence of defects called pinholes also increases, leading to decreased PCEs. To deal with this problem, the researchers increased the electrical conductivity of these layers by more than 10 times through heavily doping both electron and hole extraction layers. In this way, they fabricated layers that have fewer pinholes over wide areas and are applicable at thicknesses of up to 10 to 20 nm. Using these layers, a PCE of 16% was repeatedly attained while employing cells that were greater than 1 cm2. The use of inorganic materials also contributed to PCE reduction within 10% even after undergoing 1,000 hours of continuous exposure to sunlight at an intensity of 1 sun, demonstrating outstanding reliability.
Following these encouraging results, the researchers aim to develop more efficient light absorbing material capable of utilizing a greater amount of sunlight and precisely controlling the interfaces in the devices, for achieving higher PCEs and stability.