Interface and Morphology Engineering in Solution-Processed Electronic and Optoelectronic Devices

The first part of this dissertation focuses on interface and morphology engineering in polymer- and small molecule-based organic solar cells. High-performance devices were fabricated, and the device performance was correlated with nanoscale structures using various electrical, spectroscopic and microscopic characterization techniques, providing guidelines for high-efficiency cell design.

The second part focuses on perovskite solar cells (PSCs), an emerging photovoltaic technology with skyrocketing rise in power conversion efficiency (PCE) and currently showing comparable PCEs with those of existing thin film photovoltaic technologies such as CIGS and CdTe. Fabrication of large-area PSCs without compromising reproducibility and device PCE requires formation of dense, pinhole-free and highly uniform perovskite thin films over large area, which remains a big challenge as of today. In this work, a scalable process, called ultrasonic spray-coating (USC), was thoroughly optimized to deposit dense and uniform perovskite thin films for high-efficiency PSCs. In order to realize high-performance flexible PSCs, a unique photonic curing technique was demonstrated to achieve highly conductive TiO₂ as electron transport layer on flexible substrates. Moreover, the effect of processing conditions on perovskite film growth was evaluated and taken into account to increase PCE to more than 15%.

In addition, a series of high-performance organic field-effect transistors (OFETs) were fabricated en route to demonstrate the versatility of the USC process. Several different polymer binders were used to modulate the lateral and vertical phase morphologies in OFETs, significantly improving the device performance.

In summary, this research provides guidelines for the design and fabrication of high-performance solution-processed solar cells and field-effect transistors based on organic materials and hybrid perovskites, while presenting a viable route for large-scale fabrication.