Chemical modifications of perovskite solar cells at interfaces

Perovskite solar cells (PSCs) are an attractive renewable energy source due to their ease of solution-based fabrication, low toxicity, and high power conversion efficiency. However, defective interfaces still restrict the performance and large-scale deployment of PSCs for modern renewable energy solutions. Most prevalent modification strategies for defective PSC interfaces are restricted to material engineering of interlayers that only provide limited improvements to overall device performance. This thesis presents chemical modifications to improve the interface quality of PSCs by passivating defects and improving interfacial contacts. Furthermore, it explores the mechanisms that improve device efficiency and stability. These chemical modifications demonstrate high tunability and low fabrication complexity, which can improve device performance, inspire new interlayer designs, and facilitate further deployment of high-efficiency PSCs. This thesis first introduces the fabrication workflow of PSCs, and each layer of the device is appropriately adjusted to obtain high performance. It also introduces major characterization technologies that help study the performance and charge transport in PSCs. Sputter deposition is then introduced for scalable metal contact deposition of PSCs. This technology has not been applied previously because it damages the adjacent organic hole transport layer (HTL). However, this sputtering damage can be reversed by oxidation, and the resulting PSCs exhibit high efficiency (18.7%). Characterization results demonstrate that the oxidation step reconstructs the molecular order of the HTL and reverses Au atom diffusion into the device. The next part explores the interfacial interactions between chiral low-dimensional (quasi-2D) perovskites and chiral HTLs. ‘Chiral matching’ between ionic HTLs and perovskite enantiomers with heterochiral interactions (R + S) results in test devices with less energy loss in the hole transport and higher durability. Density functional theory calculations further support a detailed mechanistic understanding of this interface. Finally, this thesis develops a new molecular interlayer strategy at the perovskite|HTL interface using large triarylammonium cations (>6 Å). The resulting PSCs achieve higher efficiency (19.4%) than quasi-2D perovskite interlayers (18.9%) and high stability by suppressing the formation of resistive quasi-2D perovskites and improving the perovskite|HTL interfacial contact. This new strategy will inspire unique design principles for PSC interlayers.