UC Santa Cruz

Thin-film optoelectronics are an incredibly worthwhile research topic. Unsurprisingly, their thin profiles use less material than their thicker, more traditional counterparts. However, they also benefit from increased flexibility, as well as an increased array of fabrication routes. The materials investigated in this work are well poised for scalable solution processing techniques that lend themselves to a manufacturing setting.

Here, I investigate three types of optoelectronic devices: a) the photodetector, b) solar cells, and c) and light-emitting diodes (LEDs). All of these work to transform between light particles and electronic particles. My work examines, in each case, what makes for a successful device.

Beginning with germanium quantum dots, this work begins by modeling the Ge QD raman spectra as a function of particle size. To do this, we implement the confined phonon model first implemented by Richter, Wang, and Ley\cite{richter_one_1981}. We succesfully predict the extreme asymmetric broadening towards low-energy modes that is observed in data taken by collaborators.

We then implemented Ge QDs into thin-film photodetectors, using an ITO/TiO$_2$/Ge QD/Au architecture. We found a signal-to-noise a ratio greater than 10$^4$ at at 1V bias. Additionally, it was found that conductivity was improved by Ge QDs samples with increased crystallinity.

Our next study focused on thin-film organic-inorganic perovskite solar cells. Using methylammonium lead iodide (MAPbI$_3$) as our absorption layer, these devices utilize a well-studied architecture which uses PEDOT:PSS as a hole extraction layer. We find that increasingly thinner PEDOT:PSS layer results in better performing devices.

My last chapter focuses on using formamidinium lead bromide (FAPbBr$_3$) as a green-emitting active layer in an ITO/TiO$_2$/Perovksite/Spiro-OMeTAD/Au architecture. By reducing the free lead content in our system \textit{via} a nonstoichiometric precursor ratio, we find successful green emission despite increased disorder on the perovskite surface.