Larger-area (1cm2) perovskite solar cells made with the additive. Photo: City University of Hong Kong.
Larger-area (1cm2) perovskite solar cells made with the additive. Photo: City University of Hong Kong.

Perovskite solar cells (PVSCs) are a promising alternative to traditional silicon-based solar cells because of their high power-conversion efficiency (PCE) and low cost. However, one of the major challenges in their development has been achieving long-term stability.

Now, a research team from City University of Hong Kong (CityU) has made a breakthrough by developing an innovative, multifunctional and non-volatile additive that can improve the efficiency and stability of PVSCs by modulating perovskite film growth. This simple and effective strategy has great potential for facilitating the commercialization of PVSCs.

“This type of multifunctional additive can be generally used to make different perovskite compositions for fabricating highly efficient and stable perovskite solar cells,” explained Alex Jen, professor of materials science and director of the Hong Kong Institute for Clean Energy at CityU, who led the study. “The high-quality perovskite films will enable the upscaling of large-area solar panels.” Jen and his team report their work in a paper in Nature Photonics.

PVSCs have attracted significant attention due to their impressive solar PCE and their ability to be easily deposited onto surfaces as a solution. As such, PVSCs have the potential to be utilized for building-integrated photovoltaics (BIPV), wearable devices and solar farms. However, the efficiency and stability of perovskite films are still affected by the severe energy losses associated with defects embedded at their interfaces and grain boundaries. Therefore, the intrinsic quality of perovskite films plays a critical role in determining the achievable efficiency and stability of PVSCs.

Although many previous research studies have focused on using volatile additives to improve the morphology and quality of perovskite films, these additives tend to escape from the film after annealing, creating a void at the perovskite-substrate interface.

To tackle these issues, the CityU researchers developed a simple but effective strategy of modulating perovskite film growth to enhance film quality. They found that adding a multifunctional molecule (4-guanidinobenzoic acid hydrochloride (GBAC)) to the perovskite precursor caused the formation of a hydrogen-bond-bridged intermediate phase and modulated the crystallization to produce high-quality perovskite films with large perovskite crystal grains and coherent grain growth. GBAC could also serve as an effective defect-passivation linker (to reduce defect density in the perovskite film) due to its non-volatility, resulting in significantly reduced non-radiative recombination losses and improved film quality.

Experiments showed that the defect density of the perovskite films was significantly reduced after introducing GBAC. The PCE of inverted (p-i-n) perovskite solar cells fabricated using these modified perovskite films was boosted to 24.8%, which is among the highest values ever reported. Also, the overall energy loss of the device was reduced to 0.36eV, representing one of the lowest energy losses among PVSC devices with a high PCE.

Additionally, the unencapsulated devices exhibited improved thermal stability beyond 1000 hours under continuous heating at around 65°C in a nitrogen-filled glovebox while maintaining 98% of their original efficiency.

The team demonstrated the general applicability of this strategy for different perovskite compositions and large-area devices. For example, a larger-area device (1cm2) delivered a high PCE of 22.7% with this strategy, indicating excellent potential for fabricating scalable, highly efficient PVSCs.

“This work provides a clear path to achieving optimized perovskite film quality to facilitate the development of highly efficient and stable perovskite solar cells and their upscaling for practical applications,” said Jen.

In the future, the team aims to further extend the molecular structures and optimize the device structure through compositional and interfacial engineering. They will also focus on fabricating large-area devices.

This story is adapted from material from City University of Hong Kong, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.