Ready for a New Solar Cell? A Breakthrough to Replace Silicon

"Perovskite materials are designed for optical applications such as solar cells and LEDs," said Kanishka Kobbekaduwa, first author of the study and graduate student at CU, according to a Phys.org report. "It is important because it is much easier to synthesize compared to current silicon-based solar cells. This can be done by solution processing — whereas silicon, you have to have different methods that are more expensive and time-consuming."

Using an electric field to probe defects in materials

This new research aims to forge materials capable of providing more efficient power service at cheaper costs, and with simpler production methods.

And Gao's team's new method — which uses ultrafast photocurrent spectroscopy — enabled vastly higher time resolution than conventional methods — to identify the physics of trapped carriers. Trapped carriers reveal defects in a material — which help define the limits of its efficiency. In this study, the method was measured in mere picoseconds (one trillionth of a second).

"We make devices using this (perovskite) material and we use a laser to shine light on it and excite the electrons within the material," said Kobbekaduwa. "And then by using an external electric field, we generate a photocurrent. By measuring that photocurrent, we can actually tell people the characteristics of this material."

"In our case, we defined the trapped states, which are defects in the material that will affect the current that we get," explained Kobbekaduwa in the report.

How we transform our energy infrastructure can always evolve

After the physics are determined, the science moves on to seek out defects, and identify how they create inefficiency in the materials. Once reduced, the increased efficiency can greatly improve the function of solar cells or other devices.

Conventional materials — forged via solution processes like spin coating or inkjet printing — raise the probability of introducing defects. But the new low-temperature processes are cheaper than ultra-high temperature ones — which are designed to create a pure material.

The scientists fired a laser at the new material to study signal propagation. The laser method helped them monitor the current, distinguishing this study from others — who don't use electric fields.

"By analyzing that current, we are able to see how the electrons moved and how they come out of a defect," said Pan Adhikari of the UPQD group, in the Phys.org report. "It is possible only because our technique involves ultrafast time scale and in-situ devices under an electrical field. Once the electron falls into the defect, those who experiment using other techniques cannot take that out."

"But we can take it out because we have the electric field," added Adhikari. "Electrons have charge under the electric field, and they can move from one place to another. We are able to analyze their transport from one point to another inside the material."

While this is only a proof-of-concept for solution-processed perovskite materials, the implementation could offer significant advantages over silicon-based devices, like conventional solar cells. Energy infrastructures around the world will transform in the next decade, but this study is a prime example of how the way we do it can always evolve, for the better.