Hybrid materials for Si surface passivation and battery applications

The overall goal of this project has been functional materials development by hybridizing polymer with inorganic nanomaterials. The following main tasks were performed to achieve these goals: 1. Functionalization the polymer using doped and undoped Si nanoparticles, Carbon NanoTubes (CNTs) and transition metal-oxide nanoparticles as well as polymer additives and poly electrolytes; 2. Developing scalable industrially viable methods of deposition of the functional materials; 3. Understanding the mechanisms responsible for both determining the overall properties of the hybrid materials by addition of nanoparticles, as well as how they affect degradation and durability. 4. Characterization of Si/hybrid interface for solar cell applications. 5. Evaluation of applications of the hybrid materials as anode in Li-ion batteries. The project HyMatSiRen was a collaboration between research groups and companies in Norway (IFE), Turkey and Spain (UCM). The project has arranged international workshops in both Norway, Turkey and Spain, and there has been extensive exchange of students, particularly between IFE/UiO and UCM. The research in the project has also been strengthened by additional collaboration with the University of Karlstad in Sweden. In the project, we have successfully developed new processes for surface passivation with PEDOT. We have developed new, PEDOT-based materials functionalized with different nanoparticles and investigated how these affect the properties, stability and applicability of this type of materials for use in solar cells and batteries. In 2020, two M.Sc. students from IFE/UiO worked towards the project. One successfully developed hybris solar cells in collaboration with IFE staff in the IFE Solar Cell Laboratory. The other travelled to UCM for performing advanced characterization of the chemical composition and structure of the nanoparticles and the functionalized hybrid PEDOT materials. This has been a productive project. The project has given many oral and poster presentations at international conferences, 8 of which were at the important E-MRS fall meeting. One was an invited lecture there. Many of the results from this conference is now being prepared for publication in international journals. The research has also led to two additional journal publications. Researchers from the project have participated in the organization of two international conferences, one of which was the E-MRS meeting. The main conclusions from the HyMatSiRen project were as follows: - PEDOT:PSS is a promising solar cell material for high efficiency, lower cost silicon solar cells. The material properties make it a good choice both as an emitter and surface passivation layer - The surface passivation yielded by PEDOT:PSS on silicon is unstable. However, even after degradation, the surface passivation is suitable for use in efficient solar cells. - Functionalization of PEDOT:PSS with nanoparticles is a way to tailor both the electrical and optical properties of the material for specific applications.

A patent was by UCM and IFE was approved regarding the surface passivation, this secures rights to commercial exploitation of many of the important results. A simple process for surface passivation of silicon wafers using PEDOT:PSS has been developed. The stability of the surface passivation is still not resolved, but even after degradation substantial surface passivation remains. A method for fabricating samples for electrical characterization of hybrid device structures has been developed. Solar cells with high efficiency potential have been fabricated within the project. This opens up for development of new solar cell architectures incorporating PEDOT:PSS in combination with other, efficiency-enhancing processes, particularly rear side passivation and texturing. A good collaboration between IFE and UCM has been strengthened substantially in this project. The project has produced numerous scientific publications. The project has contributed to the training of PhD and M.Sc. students.

The project focuses on development of new hybrid materials incorporating inorganic nanomaterials into polymers addressing specific needs in photovoltaics (PV) and Li-ion batteries. On one hand, the unit cost of the industrial Si solar cells is limited by production steps like emitter formation using high temperature diffusion (900-1100 ºC) of phosphorus or boron within ~45 min, needed to form the pn-junction [1]. Recently, a new contender has emerged: the hybrid organic-Si solar cells, combining the advantages of the Si and polymer PV technologies. The possibility of deposition of electrically conducting polymer from solution by a coating process at room temperature opens up its use as a novel emitter layer thus avoiding the added energy costs of the conventional emitter production. However, Si surface passivation by the polymer is an important challenge to be enhanced by functionalization of the polymer. Within the collaborative preliminary work the consortium partners IFE and UCM have demonstrated that the Si/PEDOT:PSS interface can be improved by functionalizing PEDOT:PSS with inorganic oxide nanoparticles (np) and TRL of 3 has been achieved. On the other hand, during Li transport in Li-ion batteries, Si is subjected to lattice variation that causes the mechanical disintegration of Si grains and the surrounding composite electrode architecture leading to a rapid fade in the capacity and further loss of electrical contacts with the current collector or between the Si phase and the conductive matrix. Preliminary work performed by the consortium has shown that nanocomposites (ENWAIR) and hybrid materials (IFE and UCM) have the potential to solve these issues and TRL 3 is achieved. The aim of the proposal is functional materials development by hybridizing polymer with inorganic nanomaterials.