Perovskite solar cells hit record 25% efficiency with new passivation technique

A team of researchers from China and the United States have demonstrated the capability to achieve high-concentration passivation without reducing the performance of perovskite solar cells.

The researchers used a molecular passivator based on π-conjugated terpyridine Lewis-base molecules to treat perovskite solar cells.

According to the results published by the researchers, the cells achieved 25.24% power conversion efficiency, with 90% PCE retained after 2,664 hours of light exposure.

They show that the perovskite solar cells treated using this method avoids getting damaged and retain their performance.

Boosting performance of perovskite solar cells

There has been rapid progress in the use of perovskite solar cells in the past decade and the newer versions of the same have high power conversion efficiency value.

Defect passivation is thought to be one of the most effective strategies for increasing the PCE of PSCs , and a number of materials that successfully passivate defects in PSCs have been identified and studied.

However, one very big issue with the passivators is their durability, a cause which has largely been ignored.

Nothing can currently be done about the defects generated during device operation because the concentrations of passivators have always been optimized based on freshly prepared devices. This leads to them being insufficient to accommodate the newly formed defects, leading to a mismatch between the concentrations of passivators and defects.

An excess of passivator can also diminish device performance.

Therefore, in the study the researchers suggest a strategy of heavily passivating the perovskite surface with a π-conjugated passivator, the passivation effectiveness of which is not concentration dependent and can therefore be used with high initial concentrations without impacting PCE.

The process to find the perfect solution

Three organic Lewis-base molecules—pyridine, bipyridine, and terpyridine—were used to investigate the π-conjugation effect of molecular structure on passivation and its durability.

Terpyridine, which has the largest π-conjugation, proved to be the least concentration dependent and showed the best passivation durability, according to the paper published in the journal Joule .

The terpyridine-passivated PSCs in the study achieved a remarkably improved PCE of 25.24%, along with enhanced thermal and illumination stability.

The researchers demonstrated a concentration-independent passivation effect for PSCs in a rationally designed π-conjugated molecule. The concentration independence enables excess-concentration surface passivation, which enhances passivation durability as the excess passivation molecules interact with newly formed defects as devices degrade.

It also helps in designing passivation molecules with concentration independence and thus improved passivation durability.

The team believes that their work will result in increased attention to the passivation durability when designing passivation molecules in the future.

Summary

Defect passivation is regarded as an essential strategy for constructing efficient perovskite solar cells. However, the passivation in long-term operation durability has been largely ignored. Passivator concentration is usually optimized using fresh devices, whereas defect concentration increases with time during actual device operation. As a result, the initial passivators with low concentrations fail to passivate growing numbers of defects in a sustainable manner. Higher initial concentrations of passivators could in principle deal with new defects as they develop, but this strategy has not been successful so far because high concentrations of passivators are always harmful to device performance. In this study, we report a type of π-conjugated passivator, the passivation effectiveness of which is independent of its concentration. This unique feature allows for high-concentration passivation without reducing device performance, which considerably improves passivation durability. This study will provide guidance for designing concentration-independent passivators and direct attentions to their passivation durability.