Halide perovskite solar cells: an investigation of ink additives on perovskite crystallization

• Main Author: Choong, Anthony Li Yan
• Other Authors: Nripan Mathews
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/156765
• Institution: Nanyang Technological University

Perovskite solar cells (PSCs) are among the 3rd generation of solar cells which can compete with the conventional bulk silicon solar cells in terms of power conversion efficiency (PCE). They have been hotly researched over the past decade, with their high absorption coefficients, tunable band gaps and inexpensive facile fabrication processes as the main selling points. In just 13 years since the first PSC was successfully synthesised, the PCE has skyrocketed from 3.8% in 2009 to 25.8% (25.5% certified) in 2021, with plenty of research and keen interest ongoing to improve device performance; and also to achieve the ultimate goal of commercialising PSCs. However, the main drawback of PSCs is their poor stability in the ambient environment, which is well-documented and adversely impacts efforts to commercialise PSCs. The stability of PSCs has been the subject of numerous studies by many researchers who seek to prolong the stability of PSCs besides improving their PCE. In 2021, Michael Gråtzel’s group added a pseudohalide additive, formamidinium formate (FAHCOO), into formamidinium lead iodide (FAPbI3), which resulted in a then-world-record PCE for single junction PSCs at 25.6% (25.2% certified), as well as improved stability. HCOO- is one of several pseudohalide additives used to improve PCE and stability of PSCs. Other examples used include BH4-, PF6-, SCN-, and CH3COO-. Another pseudohalide, the methanesulfonate (MeSf) anion, is a potential candidate to improve the PCE and stability of PSCs. There have been very limited studies of the MeSf anion, even though Cs MeSf was studied before on quasi-2D PSCs. Thus, there is a high degree of novelty in using MeSf. In this project, FA MeSf was used as the additive to FAPbI3 to investigate the effects of the MeSf anion in improving the efficiency and stability of FAPbI3. With the addition of 1 mol% FA MeSf, there is a retardation in the α-to-δ phase transformation, as well as an improved PCE of 19.63%, as compared to the control devices (17.35%). Moreover, the addition of 1 mol% FA MeSf improved the shelf life and thermal stability of FAPbI3. In particular, a higher normalised PCE of 93.8% was achieved after more than 450 hours of storage at 25°C, 35% RH in the dark as compared to the control devices (80.5%). The addition of 1 mol% FA MeSf also resulted in the highest contact angle of 47.76° and hence, the highest amount of moisture stability. Although a higher normalised PCE was also achieved after more than 250 hours of storage at 65°C, and approximately 15% RH (47.8% vs 15.9%), there is still room for improvement in the thermal stability of FAPbI3. Thus, for future outlooks, encapsulation of the PSCs could be performed to provide further protection.