Because of its excellent power-conversion efficiency and low price, perovskite solar cells (PVSCs) are a possible replacement for conventional silicon-based solar cells. Nevertheless, ensuring long-term stability has been one of the main obstacles in their development.
A research team from the City University of Hong Kong (CityU) recently achieved a breakthrough by creating a novel, multifunctional, non-volatile additive that can enhance the stability and efficiency of perovskite solar cells by controlling the growth of the perovskite film. The commercialization of PVSCs has a lot of potential because to this straightforward and successful technique.
“This type of multifunctional additive can be generally used to make different perovskite compositions for fabricating highly efficient and stable perovskite solar cells. The high-quality perovskite films will enable the upscaling of large-area solar panels,” explained Professor Alex Jen Kwan-yue, Lee Shau Kee Chair Professor of Materials Science and Director of the Hong Kong Institute for Clean Energy at CityU, who led the study.
A lot of interest has been paid to PVSCs because of their outstanding solar power conversion efficiency (PCE). PVSCs have the potential to be used in solar farm applications, wearable technology, and building-integrated photovoltaics (BIPV) because perovskites can be deposited from solutions onto the manufacturing surfaces.
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.
Professor Alex Jen Kwan-yue
The substantial energy loss associated with flaws imbedded at the interfaces and grain boundaries of the perovskites, however, continues to have an impact on the efficiency and stability. Therefore, a key factor in determining the stability and efficiency of PVSCs is the inherent quality of the perovskite layer.
Although numerous earlier investigations concentrated on using volatile additives to enhance the film shape and quality, these compounds frequently escape from the film after annealing, leaving a void at the perovskite-substrate interface.
To tackle these issues, the CityU researchers developed a simple but effective strategy of modulating the perovskite film growth to enhance the film quality. They found that by adding a multifunctional molecule (4-guanidinobenzoic acid hydrochloride, (GBAC)) to the perovskite precursor, a hydrogen-bond-bridged intermediate phase is formed and modulates the crystallization to achieve high-quality perovskite films with large perovskite crystal grains and coherent grain growth from the bottom to the surface of the film.
Due to its non-volatility, this molecule can also be used to effectively remove defects in perovskite films that have been annealed, leading to a reduction in non-radiative recombination loss and an improvement in film quality.
Their research demonstrated that adding GBAC can drastically lower the defect density of perovskite sheets. The power conversion efficiency of inverted (p-i-n) perovskite solar cells based on the modified perovskites was boosted to 24.8% (24.5% certified by the Japan Electrical Safety & Environment Technology Laboratories), which is among the highest values reported in the literature.
Also, the overall energy loss of the device was reduced to 0.36eV, representing one of the lowest energy losses among the PVSC devices with high power conversion efficiency.
Additionally, the unencapsulated devices exhibit improved thermal stability beyond 1,000 hours under continuous heating at 65 ± 5°C in a nitrogen-filled glovebox while maintaining 98% of the original efficiency.
The group showed how this approach might be used generally for various perovskite compositions and large-area devices. For example, a larger area device (1 cm2) in the experiment 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 Professor Jen.
Through compositional and interfacial engineering, the team hopes to improve the device structure and further the molecular architectures in the future. They will also focus on the fabrication of large-area devices.
The findings were published in the scientific journal Nature Photonics under the title “Hydrogen-bond-bridged intermediate for perovskite solar cells with enhanced efficiency and stability.”
Professor Jen is the corresponding author of the research. The co-first authors are Miss Li Fengzhu and Dr. Deng Xiang from Professor Jen’s research group.
Other team members from CityU include Dr. Chen Xiankai, Dr. Tsang Sai?wing, Dr. Yang Zhengbao, Dr. Francis Lin, and Dr. Wu Shengfan. CityU, the Innovation and Technology Commission, the Research Grants Council, the Green Tech Fund of the Environment and Ecology Bureau in Hong Kong, the Guangdong Major Project of Basic and Applied Basic Research, and the Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials, supported the research.
