Quantum Dots Searching for Bondots: Towards Sustainable Sensitized Solar Cells

Introduction

Renewable and sustainable technology is the main and the aim in the XXI^th century; this not only because of the economic research, but also for maintaining the global balance between ecosystems and society, including social and global peace, threatened otherwise by a higher and higher energetic demand, by increasing the population number while decreasing the natural resources (Service 1996). On the other hand, physics and chemistry successfully combined their fundamental principles in what was established as nanoscience, immediately turned into nanotechnology by algorithmic contributions and engineering implementations. This way, what is naturally treated as water, earth, air and fire, and their traces in entropic activity/interaction, are converted in the terms of renewability, conversion, and sustainability (Putz & Mirica, 2016). Precisely, the fire appears as light and seems to be less affected from industrial or home pollution process, this way presenting the highest degree of renewability, conversion, and sustainability, to be handle by nanoscience and nanotechnology. Moreover, this way the phenomenological, conceptual and applicative connections between the electromagnetic radiation/solar radiation (photons-bosons) and the structure mater by electrons (fermions) constitute the most important interaction of which control can assure the sustainable future of the humankind (Markvart, 2005).

In this context, the photo-electro-chemical phenomena is already placed in its third century of study and in the third generation of accomplishment (see Figure 1) and application. Regarding its discovering: it started in 1839 with Becquerel communication about photo-potential/ photo-voltage observed at an electrode under the light influence in electrolytic bath/solution; similar effects were noted also in 1870 and 1900 with solid selenium as electrolytic material, though with a conversion/efficiency effect of about 1%; only after another 50 years Daryl Chapin raised the photo-electro efficiency up-to 6% with a silicon cell, with further increasing to 14% and then to 30% for GaAs multi-junction; this way, the inorganic photovoltaic cells era was opened with 20^th century applications in satellites implants (starting with Vanguard I in March, 1958), as well as in security developing. Still, these cells proved to be very expensive in fabrication and with a relative fragility (Messenger & Ventre 2004).

Figure 1.

The three generations of photovoltaics/solar cells in relation with the solar light-electrical energy conversion efficiency in conventional costs (US dollars) on <Watt> and <m²> respectively, in the fabrication technology; there are marked> the physical limits of the excitation band (HOMO-LUMO) on the cell’s sensitizer coupled to the photo-electro-chemical cell anode (Shockley & Queisser 1961); the thermodynamic limit (entropy, at infinite temperature); and the actual solar cell with quantum dots (QD)

Redrawn and adapted after Kouhnavard et al. (2014), Jun et al. (2013).