Organometal trihalide perovskite solar cells with conversion efficiencies of 20.1%

Fast forward to 2015 and silicon-based solar panels are ubiquitous. They have become an indispensable means of generating energy for human habitats, space exploration, and wearable devices such as wrist watches.

Now, at the research level, scientists are innovating to produce even more efficient solar cells at low cost, using environmentally friendly materials. Notably, recent reports of solar cell conversion efficiencies of 20.1% for cells fabricated using organometal trihalide perovskite have caught the imagination of scientists in the search for high performance, cheap solar cells.

"This very high 20% efficiency exhibited by organolead halide perovskite solar cells has galvanized scientists to focus on understanding the physics of this material system," says Qing Shen, associate professor at the Department of Engineering Science, Faculty of Informatics and Engineering at UEC. "Two of the main issues to resolve are clarifying why organolead halide perovskites yield such a high efficiency, and potential alternatives to lead based perovskites."

The material properties governing the high conversion efficiency of perovskite-based organic/inorganic solid state solar cells (OIHSCs ) include their direct band gap and high optical absorption; large dielectric coefficient leading to smaller exciton binding energy; long photoexcited carrier lifetimes; no deep level defects; and very small Urbach energy.

"Our research is focused on clarifying the physical properties of this material that are responsible for such a high conversion efficiency," says Shen. "More specially, we are studying the relationship between carrier lifetime, charge separation and charge recombination dynamics and the performance of photovoltaic perovskite-based OIHSCs."

Shen has developed a dedicated transient absorption (TA) system to measure charge separation and recombination dynamics from the sub-picoseond to milli-second range. Recent experiments shows perovskite CH3NH3PbIxCl3-x to show long carrier lifetimes in the micro-second range and charge separation efficiency of TiO2/CH3NH3PbIxCl3-x/Spiro to be as high as 90%.