Interfacial engineering and molecularly designed additive for stable perovskite solar cells

• Main Author: Bening Tirta Muhammad
• Other Authors: Leong Wei Lin
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Science::Chemistry; Engineering::Materials::Energy materials; Engineering::Materials::Nanostructured materials
• Online Access: https://hdl.handle.net/10356/155777
• Institution: Nanyang Technological University

The past decade has witnessed the rapid development of halide perovskite-based solar cell (PSC) performance. With several spin-off companies had been founded to expedite the commercialization of PSCs, stability remains the bottleneck to market this new technology with high confidence. Despite growing size of literature body investigating stability aspects of PSCs, there are several questions seem scarcely discussed or even visited. Firstly, with strong reliance to metal-oxide based carrier selective contacts or transport layers, metal oxide/perovskite interfaces are inevitable, and their interfacial stability should be examined in-depth. In response, it is hypothesized that even with relatively acidic TiO2, metal oxide/perovskite interface is susceptible to protonation reaction by organic A-site cation at elevated temperatures. To overcome that, metal oxide surface was functionalized with sulfate moieties. This study shows that sulfate functionalization suppresses the amount of hydroxide groups inherently present on metal oxide surface and cuts off the pathway to perovskite’s A-site deprotonation. Secondly, there has been also a wide variety of metal oxide-based transport layer precursors, from ethanolic solutions to aqueous colloidal dispersions, that do not seem converging to one or a few established recipes any time soon. However, in term of colloid-based metal oxide precursors, the relationship between colloidal particle size and resulting transport layer’s morphological and electrical properties has hardly been investigated. Here, size tunable SnO2 nanoparticle precursor synthesis was reported and different nanoparticle sizes were applied to act as interfacial layer between TiO2/perovskite in planar PSCs. The results show that the smallest size gives rise to the best charge carrier transport property and accordingly device performance. Lastly, reports on moisture-resistant PSCs are mainly realized by hydrophobic doping, surface treatment, and encapsulation techniques. At the same time, there emerge few reports that suggest hydrophilic moieties could also improve stability in humid atmosphere. However, studies combining the best of both worlds are yet to be seen. Here, we utilize molecular design principles and come up with a novel amphiphilic molecule called Cor-TEG which is a marriage between hydrophobic aromatic corannulene sulfone and hydrophilic triethylene glycol side chains. Cor-TEG is introduced as dopant to perovskite precursor solution. Our study demonstrates that adding a minute amount of Cor-TEG to perovskite precursor solution results in enlarged perovskite grains, improved charge transport property and enhanced and moisture resistance that can be attributed to Lewis base sites, delocalized electrons in the aromatic core, and the hydrophilic side chains, respectively, present in a single molecule.