Ph.D Thesis

Ph.D StudentDinner Omry
SubjectSol-Gel Synthesis of Indium Doped ZnO TCO and Route to
its Efficient Incorporation in Perovskite
PV Cells
DepartmentDepartment of Chemical Engineering
Supervisor PROF. Gideon Grader
Full Thesis textFull thesis text - English Version


Today, more than ever, low cost and renewable energy sources are needed due to the increase of worldwide population and energy demands, depletion of fossil fuels, changes in world climate and, in particularly, the worsening in greenhouse effect. Reliable and efficient Photovoltaic (PV) cells will be part of the solution to deal with these challenges.  PV cells can be designed to absorb various parts of the solar spectrum, near-IR, visible and near-UV or all of these.

Over the last 35 years, the PV cell efficiency has improved dramatically.  In particular, the efficiency of multi-junction PV is higher than 40%. However, the manufacturing cost of most PV cells is relatively high (especially of high efficiency cells), giving rise to a considerably higher $/W level than that of conventionally generated electricity. Therefore, alternative routes to reduce the cost of PV-based electricity are needed. A new promising type of PV cell has emerged with an active layer consisting of organo-metal trihalide perovskites. Therefore, research of the materials than make out these new type of PV cells is a crucial step to turn them into a viable commercial option. This research dealt with the preparation of indium doped zinc oxide films via solvothermal synthesis of nano-particles, followed by spin coating of the TCO. The influence of the In/Zn molar ratio on the lattice parameters and the cell volume was determined by XRD analysis. In addition, the effect of the molar ratio on the optical and electrical properties was studied. A minimal sheet resistance of <46Ω/sq and transparency of >85% at In/Zn=0.04 were achieved. Next, MAPbI3-xClx layer was prepared and deposition on IZO/ZnO substrate. A denser layer with a cubie like structure was successfully achieved. In addition, the best cell was obtained with an efficiency=1.86% and VOC=0.8V.

In addition, a unique structure of a thin layer consisting of cesium iodine, manifested by a “ladder-like” fractal structure formed by spin-coating was investigated in this research. The ladder-like structure is made of mm-size domains, each comprising of a highly correlated, perpendicularly interconnected, network of CsI lines. Each line served as the growth origin of 2-3 levels of short, perpendicularly-oriented CsI crystals. The observed structure differs from common Diffusion Limited Aggregation shapes by the absence of any morphological indicators that may point on the origin of growth. A formation mechanism is presented, based on studying the evolution of this structure at different spinning rates and on a variety of substrates. It is proposed that this unique structure originates from a rare combination of conditions: strong anisotropy in surface energy between different facets arising from the primitive ionic crystal of CsI, the strong water-breaking property of cesium ions and an unusual effect of mesoporous substrates in preventing premature nucleation.

Bismuth based perovskite solar cell was prepared and deposited on-to FTO/TiO2 substrates. It was found that in the 2-step method BiI3 could be successfully transported to the CsI layer and reacted to Cs3Bi2I9. In addition, a dense layer of Cs3Bi2I9 phase was obtained with a hexagonal morphology. The best cell with Voc=0.72V, Jsc=3.08mA/cm2 and PCE=1.4% was achieved.