Feb 27 2018
A study indicating the way to develop high-efficiency solar cells, which are more stable compared to devices made earlier by using related materials, has been reported in Materials Today.
Investigations on the use of perovskite materials for developing solar cells have increased in the past years, subsequent to reports of high energy conversion efficiencies, which have been steadily increasing. An innovative study reported in the Materials Today journal indicates the way to enhance the service life of the solar cells.
In spite of a spurt in interest in developing materials for solar energy applications, “improving the stability of perovskite solar cells is a challenging task,” explained Dr Chang Kook Hong, corresponding author of the study, from Chonnam National University in South Korea.
Perovskite is the common terminology used to describe any mineral with the crystal structure similar to that of a specific form of calcium titanium oxide, first discovered in 1839 in the Ural Mountains of Russia and named after L. A. Perovski, a Russian mineralogist. The distinctive structure of perovskites can be adapted for specific characteristics by altering the various anions and cations with which they are made of. Basically, the common chemical formula of the structure is ABX3, where “A” and “B” indicate positively charged metal ions, or cations, that are largely distinct in size, and “X” is a negatively charged anion that gets linked to both the metal cations, connecting them together in the crystal.
Perovskites can be inexpensively produced in the lab and developed into thin films that can be introduced into solar cells. It is not necessary that the cations have to be metal ions. They can be any positively charged ion, for example, an organic ion or an ammonium ion. If the sizes of A and B are different and an appropriate negative ion is used, they will result in the perovskite structure.
Dr Hong and his team have devised a technique called co-precipitation to develop a thin film including nanoporous nickel oxide as the hole transporting layer (HTL) in a perovskite solar cell that adopts the distinctive composition of methylammonium lead bromide (MAPbBr3) and/or formamidinium lead iodide (FAPbI3) as the perovskite layer. In the field of electrochemistry, holes are regarded to be the positive equivalent of negative electrons in. Furthermore, the researchers used an organic air-stable inorganic zinc oxide nanoparticles compound as the electron transporting layer (ETL) to prevent the contact of the perovskite layer with air.
We successfully optimized the metal oxide based HTL and ETL protecting layers for highly efficient perovskite absorber by a simple method which can make air-stable photovoltaics. Our main goal is to solve the problem of the tedious process of making conventional additive-doped, highly expensive, unstable HTLs by replacing low-cost, inorganic air-stable p and n-type metal oxides.
Dr Mali, Chonnam National University
Initial investigations of the prowess of their device by adopting the perovskites device architecture exhibited a power conversion efficiency of 19.10% (±1%). The device had a current density of nearly 23 mA/cm2 and could produce 1.076 Volts. Of significance was the fact that the device had the ability to preserve four-fifths of this efficiency level in use for nearly five months.
The researchers propose that their strategy could open the door to high-efficiency air-stable perovskite solar cells.
This technique is limited to the laboratory scale, however large-scale fabrication should also be possible with this device architecture.
Dr Chang Kook Hong, Chonnam National University