Solar Fuels

Project 1: Solar-thermal conversion

PI: Peng Wang, Frederic Laquai, Derya Baran

Solar-thermal conversion, in which photothermal materials are employed to harvest sunlight and convert it to heat as terminal energy for beneficial usage, has recently gained renewed research interest due to its extremely high-energy efficiency. The goal of this new seed project is to develop flexible and mechanically strong polymer-based photothermal materials with high energy conversion efficiency toward practical application especially photothermal water desalination. Two separate approaches will be explored:

  1. Embedding lost-cost carbon-based photothermal materials (e.g., carbon black, carbon nanotubes, graphene) into an inactive polymeric matrix. The polymeric materials are expected to be stable in water under solar irradiation and their refractive index should be between water and these active inorganic materials so that no light reflection loss will occur.
  2. All-polymeric photothermal materials. In this approach, we will explore a variety of conductive polymers and semi-conductive polymers with narrow band gaps with a clear aim to identify the ones with high water and light stability as well as high energy conversion efficiency.  Electrospinning will be employed to make polymeric fibers in both cases, which will be packaged along with heat barrier into all-in-one devices for performance investigation. 

Project 2: Highly efficient water splitting of Si photoelectrodes achieved by concurrent design of optical and electrical engineering

PI: Jr-Hau He, Stefaan De Wolf

The main objective of this proposal is to develop a high-performance and stable Si-based integrated PEC system that can be successfully transformed to industrial prototypes. High quality textured crystalline Si solar cell with a buried junction (homo- and heterojunction) will be employed for this purpose. The overall PEC process consists of two parts: (i) light absorption and the charge carrier generation, and (ii) the extraction of excited carriers to drive the chemical reactions. Hence, it is essential to harvest the most part of the solar spectrum while ensuring efficient charge separation. As an example for the lack of better PEC designs, all the Si photoelectrodes reported, so far are based on the light illumination from top side despite the fact that Si is the bottom layer in the PEC cell and therefore the investigations with light illuminated from the rear side is critical. In real world applications, both the front- and rear-side light absorption (termed as bifacial PEC cells) is critical as the scattered and back-reflected light absorption has been shown to yield higher efficiency in the solar cells. Hence the combined effect of bifacial illumination can be crucial, which has not been investigated in PEC so far. Furthermore, it is expected that the apparent motion of the sun, changes the angle at which the direct component of light impinges on the PEC devices. Hence, the omnidirectional light harvesting capability of PEC devices becomes a major criterion to effectively capture the scattered sunlight during hazy/cloudy days. Up to date, very few studies have been devoted to understanding the omnidirectionality of PEC cells. It is crucial to evaluate the omnidirectional PEC characteristics especially for bifacial PEC systems for realizing the industrial prototype reactor. Most of the PEC devices in current literature are single-sided with poor omnidirectional light harvesting capabilities, that lacks the scalable light trapping structures. Therefore, it is of urgent necessary to design an efficiently distributed scheme for balancing those characteristics for achieving the best STH efficiency.

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