# PolyU found uneven charge loss between grains ages perovskite cells; treated cells kept 90% efficiency for 2,200 h

- Published: 2026-11-06 06:29 UTC
- Section: Power & Energy › Energy
- Tags: perovskite solar cells, photodegradation, grain boundaries, crystal facets, m-F-PEABr, T90 lifetime, PolyU, Watt journal, formamidinium vacancies
- URL: https://realtech.media/news/rt-79cf437a7a3e3d5135d5a5f1_polyu_found_uneven/

**Hong Kong Polytechnic University researchers identified uneven charge losses at grain boundaries as a cause of light-induced ageing in perovskite solar cells. A boundary additive extended T90 lifetime beyond 2,200 hours.**

![PolyU found uneven charge loss between grains ages perovskite cells; treated cells kept 90% efficiency for 2,200 h](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/3cb5d176b660ee4d.jpg)
*polyu.edu.hk*

A research team at The Hong Kong Polytechnic University (PolyU) has found a previously overlooked cause of ageing in perovskite solar cells exposed to light, according to polyu.edu.hk. The study was led by Prof. Yang Guang of the Department of Electrical and Electronic Engineering together with a team from Zhejiang University, and was published in the journal Watt. [1]

Perovskite cells are efficient, low-cost and lightweight, but their performance gradually declines under long exposure to sunlight. This photodegradation remains a major barrier to large-scale commercialisation, since panels must work outdoors for many years. [1]

## Uneven charge loss at grain boundaries

The electricity-generating layer consists of tiny crystals called grains, each with a particular surface orientation, its crystal facet. In mixed-facet cells, grains with different facets sit side by side, and the places where they meet are grain boundaries. Electrons and holes produced by sunlight can be trapped by defects at these boundaries and cancel each other out, which wastes energy and gradually damages the cell. [1]

The team found that where grains with (100) and (111) facets neighbour each other, charge losses on the two sides of the boundary are uneven. The (111) side has more defects, mostly vacancies where formamidinium (FA) ions should be. As a result, holes build up abnormally on that side. [1]

The (111) facet is naturally more resistant to light ageing. Even so, the hole build-up makes (111) grains degrade faster and turns them into a source of ageing. According to the authors, a cell's lifetime depends not only on the stability of each grain but also on how neighbouring grains interact. [1]

## Repairing the boundaries

To address this, the team added 3-fluorophenylethylammonium bromide (m-F-PEABr). Its molecules are too bulky to enter the grains, so they collect at the grain boundaries. The positively charged end of each molecule takes the place of missing FA ions and fills the vacancies at the (111) boundaries, while the fluorine-containing part holds the molecule in place. Charge losses on both sides then become balanced. [1]

Cells treated this way reached a power conversion efficiency of 26.55%. They retained over 90% of their initial efficiency after more than 2,200 hours of continuous operation under light equivalent to one sun, a measure known as T90 operational lifetime. [1]

Prof. Yang said previous work mostly focused on reducing the number of defects, and that this study shows for the first time that uneven charge losses between neighbouring grains are a key cause of ageing during operation. Prof. Nam-Gyu Park of Sungkyunkwan University, Korea, commended the work in a research highlight in the same journal. [1]

## Sources

1. [polyu.edu.hk](https://www.polyu.edu.hk/rio/news/2026/20261104---polyu-research-uncovers-hidden-cause-of-ageing-in-perovskite/?sc_lang=en)
2. [EurekAlert](https://www.eurekalert.org/news-releases/1150600)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-79cf437a7a3e3d5135d5a5f1_polyu_found_uneven/