Improved photostability of metal halide perovskites by microstructure modulation for photovoltaic application

Significance 

Metal halide perovskites have been increasingly used in fabricating photovoltaic devices, also known as perovskite solar cells (PSCs), owing to their excellent optoelectronic properties and record-high power conversion efficiency (PCE) exceeding 25%. Unfortunately, they suffer from poor photostability when exposed to real-scenario operating conditions, which is the main hindrance to the commercialization of PSCs. From previous research, several factors causing poor photostability in PSC, most of which are attributed to the complex variation of perovskite under continuous light irradiation, have been identified. Among them, phase segregation and photo-induced ion migration have been revealed to be the most conspicuous causes. Its significant influence on the building field leads to a remarkable reduction in the photostability of photovoltaic devices.

In general, the instability properties of PSCs during both storage and test are mainly attributed to the multiple photo-induced impacts in perovskite films. Extensive research efforts have been devoted to finding feasible methods for suppressing ion migration and reducing the lattice distortion induced by the excited carriers to improve the stability properties and photovoltaic performance of PSCs. Although replacing the light unstable components in perovskite films with stable ones is a promising approach for improving the stability properties of perovskites, poor photostability remains a big problem that warrants more intensive research.

Herein, Dr. Cong-Cong Zhang and Professor Hiroyuki Okada from the University of Toyama in collaboration with Dr. Shuai Yuan, Professor Kai-Li Wang and Professor Zhao-Kui Wang from Soochow University demonstrated a step-by-step process for addressing the problems related to photostability, photovoltaic performance and reproducibility of PSCs. To achieve these goals, the authors modified the chemical components of the perovskite precursor solution by adopting the Lewis bases thiourea as an intermediate regulator. The moisture content during the operation was also changed to minimize the formation of film voids. Their work is currently published in the research journal, Organic Electronics.

The research team showed that the adoption of the thiourea and changing the moisture content not only slowed down the perovskite nucleation process but also minimized the film voids that cause open circuit voltage and short circuit current loss. This resulted in the formation of larger grain sizes and fewer grain boundaries characterized by restrained photo-induced ion migration and fewer migration channels. Ultimately, perovskite devices with superior photostability, high test reproducibility, longer lifetime and excellent photovoltaic performance were obtained under prolonged radiation.

The results revealed that the grain size of the perovskite films and the presence of water vapor during their operation are the main factor affecting the photostability of the perovskite device. A unique change in the morphology of the perovskite film was reported at extra thiourea concentrations. For instance, despite the consistent grain-enlargement effects of adding appropriate thiourea doping amounts as shown in the literature, the grain sizes of perovskite films became relatively smaller after the addition of 7% molar ratio of thiourea.

In summary, the authors demonstrated the possibility of improving the photostability properties of metal halide perovskites for commercial photovoltaic application via microstructure modulation. Through this modification strategy, PSCs with superior photostability and photovoltaic performance were obtained. Interestingly, this strategy is versatile and applicable to perovskite films fabricated via one- and two-step methods. In a statement to Advances in Engineering, Professor Hiroyuki Okada, the lead author stated that their findings provided valuable insights for improving the stability and performance of PSCs for commercial applications.

About the author

Hiroyuki Okada
Professor: Department of Nano and Functional Material Science,
Graduate School of Science and Engineering for Research,
University of Toyama, Toyama Japan.
Email : [email protected]
Research Gate Link

Education:
Doctor of Philosophy (PhD) In Electron Device Engineering 1988,
Tokyo Institute of Technology Japan

Academic Experience:
1988 to 1991: Researcher Sumitomo Electric Industries, Japan
1991 to l 1994: Lecture Toyama University, Japan
1994 to 2005: Associate Professor Toyama University, Japan
2008 to present: Professor University of Toyama, Japan

Research Interest:
We are interested in evaluation of electro-optical properties for organic electronic materials, alignment control of organic molecules and nano-patterning technology, application of electrooptic devices using organic semiconductors. Our research fields are organic light-emitting diode (OLED) including core-shell type quantum-dot light emitting device, organic field-effect transistor (OFET), organic photovoltaic cell (OPV), flexible device, printable electronic device, and liquid crystal display (LCD). I am now studying photon quantum computing. This topics will be appeared at homepage.

Academic Society Affiliations:
Society for Information Display : Japan
Japan Society of Applied Physics : Japan
Institute of Electronics, Information and communication Engineers : Japan
Japan Liquid Crystal Society : Japan

Reference

Zhang, C., Yuan, S., Wang, K., Wang, Z., & Okada, H. (2022). Improved photostability of metal halide perovskites by microstructure modulation for photovoltaic applicationOrganic Electronics, 101, 106380.

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