Three-dimensional nanostructure-based cost-effective perovskite solar cells with enhanced performance

Abstract

The newly emerged perovskite is a promising candidate as the photon absorber. Over the past seven years, the PCE of PSCs has increased at an unprecedented rate, with efficiency currently touching 25.2% (certified) in 2019. The exponential progress can be attributed to the excellent photo-electronic properties of perovskites, including high carrier lifetime, long diffusion length, high light absorbance, etc. Its low-temperature processability reduces the energy cost of manufacturing. Despite years of research, sufficient absorption is still one of the foremost concerns for high-performance photovoltaics. Meanwhile, considering applications such as power-generating windows wearable and portable power supply, optical appearance, efficiency, longevity, and flexibility are the main concerns before its real-life application. The investigation of PSCs with long-term stability is implemented via an engineering blend ratio of halides and encapsulation perovskites with PAM. The modified device exhibited appealing tolerance against moisture and solar irradiation. This thesis studies MEIS for light-trapping photons in the wavelength range where the human eye is less perceptive. This biomimetic structure simultaneously contributes to improving the performance and visual appearance of ST-PSCs. Consequently, a record high figure-of-merit for ST-PSCs, defined as the product of PCE and average visible transmittance, is achieved. Meanwhile, the optical appearance is converted to a desired near-neutral color after introducing the MEIS. The investigation of ST-PSCs with long-term stability is implemented via the engineering blend ratio of halides. The modified device exhibited appealing tolerance against moisture and solar irradiation. This thesis studies highly periodic 3D PNW-based flexible photovoltaics possessing a core-shell structure. The vertically-aligned PNW arrays demonstrate up to 95.70% and 70.10% absorption at peak and under an incident angle of 60°, attributed to improved light absorption and efficient charge collection. Furthermore, the orthogonal carrier collection facilitates PNW-based cells to achieve high EQE (~90%) for broadband wavelength. PNWs have been successfully implemented in flexible solar cells. Intriguingly, it is discovered that the device structure can significantly help strain relaxation, thus rendering the devices possess excellent flexibility. Meanwhile, PAM protects PNWs against water and oxygen intrusion and thereby imparts robustness and long-term stability to the photovoltaic devices. Compared to their thin-film counterpart, the improved light absorption, carrier collection, stability, and superior tolerance to mechanical stress/strain enable our unique PNW-based device to provide efficient solar to electricity conversion while undergoing mechanical bending. In addition, multi-layered materials in the randomly oriented polycrystalline thin-film lead to ineffective carrier transport and collection, hindering the process of achieving high-performance solar cells. This thesis tackles this issue by producing the 3D heterojunction BiI₃ nanosheets solar cells, which embed vertically aligned monocrystalline BiI₃ nanosheets into spiro-OMeTAD. The preferred orientation of BiI₃ nanosheets and large p-n junction areas of 3D heterojunction structure enables strong light absorption and effective carrier transport and collection. Thus, a PCE of 1.45% is achieved. This PCE is the highest ever reported for BiI₃ based solar cells to our best knowledge.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Zhiyong FAN (Supervisor)