Regulation of crystallization dynamic rendering highly efficient narrow-bandgap perovskite solar cells

Chen, Guocong (2024). Regulation of crystallization dynamic rendering highly efficient narrow-bandgap perovskite solar cells. University of Birmingham. Ph.D.

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Abstract

Perovskite solar cells (PSCs) have attracted increasing interest during the last decade due to their great potential to make full use of solar energy at low cost. Among all kinds of PSCs, narrow-bandgap perovskite solar cells are theoretically able to achieve efficiency approaching the S-Q efficiency limit. However, the uncontrolled crystallization process becomes one of the significant obstacles to realizing high-quality narrow-bandgap perovskite films and achieving highly efficient PSCs. In this thesis, I present my study on regulating crystallization dynamics of narrow-bandgap perovskites, including pure \(\alpha\)-FAPbI\(_3\) perovskite and mixed tin-lead perovskites (TLPs), to produce perovskite films with improved crystallinity and suppressed defect density and, therefore, realize impressive improvements in the efficiency of PSCs. I first developed a coordinator replenishment strategy by utilizing tetramethylurea (TMU) as a coordinating agent to facilitate the pre-nucleation of \(\alpha\)-FAPbI\(_3\) perovskite crystals and, thus, regulate the crystallization dynamic of the \(\alpha\)-FAPbI\(_3\) perovskite film in an air atmosphere. This led to the remarkable improvement in crystallinity, orientation, defect density, and lattice strain of the \(\alpha\)-FAPbI\(_3\) perovskite films. As a result, the PSCs based on such perovskite films have achieved the highest efficiency of 23.2%, along with enhanced long-term stability. Then, I investigated strategies to improve the film quality of TLPs. We introduced 3,4-dihydroxybenzylamine hydrobromide (DHBABr) as an additive, which was demonstrated to preferentially coordinate with SnI\(_2\) in the precursor. Consequently, the DHBABr additive balanced the crystallization rate of both Sn- and Pb-based perovskite components during their anti-solvent treatment and annealing processes, realizing TLP films with homogeneous Sn/Pb distribution, higher crystallinity, and lower defect density. The PSCs based on such TLP films finally achieved enhanced efficiency of 22.44% and improved long-term stability. Lastly, I have also explored a templated-growth approach for the regulation of the crystallization dynamic of TLPs by utilizing 2-phosphonoethan-1-aminium iodide (2PEAI) as an additive. The 2PEAI additive was determined to selectively coordinate with SnF\(_2\) and form a SnF\(_2\)-2PEA adduct, which regulates the crystallization by templated-anchoring the perovskite components. As a result, TLP films with higher crystallinity and lower defect density were obtained. Benefiting from the improved TLP film quality, the corresponding PSCs achieved the highest PCE of 21.95%. In all these research works, the mechanisms of the regulation of crystallization dynamics were comprehensively studied and discussed.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):