Dopant-Free Silicon Solar Cells
APP develops high-efficiency, low-cost, large-area dopant-free silicon solar cells.
Electromagnetics and electrical simulation of solar cells
Recent studies on light-trapping in solar cells have been primarily based on either optical simulations, or fabrication of light-trapping various structures (nanowires, nanoholes, nanocones, etc) and absorption measurements. However, design of an efficient solar cell must consider both the electromagnetic wave propagation and carrier transport properties simultaneously. In APP, we perform combined electromagnetic and carrier transport simulations of solar cells to gain insights on the optimum light trapping structures, and doping and contact schemes. Various loss mechanisms (surface, bulk and Auger recombinations), mobility decrease and band gap shrinking with doping are being implemented in our models. We are aiming at extending our model to heterojunction solar cells.
Organic-inorganic perovskite materials have been introduced as the new class of low cost photovoltaic devices to have the promise to compete with current commercialized inorganic solar cells. The unique optoelectronic properties of perovskite absorber layer stem from its desirable band gap, high absorption coefficient over a broad visible range of the sunlight spectrum and from the high minority carrier lifetime and mobilities within the material. Among all, CH3NH3PbI3 has emerged as highly attractive perovskite material used in PV researches with already various fabrication protocols and a favorite direct band gap of 1.55 eV. In APP together with Gunbas Lab, along with solution processing method, we use thermal co-evaporation technique to prepare CH3NH3PbI3. This technique offers good crystallinity, morphology, uniformity and high reproducibility, which is particularly suitable for large-area applications. Moreover, due to its band gap tunability, we have been using perovskite in tandem with crystalline Si in order to harvest more of the sunlight spectrum leading to higher Jsc and Voc and consequently higher efficiencies.
Liquid Phase Epitaxy of Germanium on Silicon
Germanium is a group IV element compatible with CMOS fabrication technology and provides infrared photodetectors and high-speed transistors with the advantage of its smaller band gap and higher carrier mobility compared to silicon. It can also be used as a substrate for the growth of III-V compounds on silicon due to lattice-matching. These benefits can be achieved by growing crystalline germanium on silicon, which is a low cost CMOS material. In APP, we are studying the formation of single crystal germanium on insulator layers using liquid phase epitaxy enabled by crystalline silicon seed layer and rapid melting. Effects of the seed window, insulator and capping materials are also aimed to be investigated.