• Energy Research

Abstract An alkaline earth boro-aluminosilicate glass (Eagle XG), a soda-lime glass, and a light-weight polyethylene-terephthalate (PET) foil, used as typical substrates for photovoltaics, were treated by an energetic proton beam (3 MeV, dose 106–107 Gy) corresponding to approx. 30 years of operation at low Earth orbit. Properties of the irradiated substrates were characterized by atomic force microscopy, optical absorption, optical diffuse reflectance, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and terahertz (THz) spectroscopy. Minimal changes of optical and morphological properties are detected on the bare Eagle XG glass, whereas the bare PET foil exhibits pronounced increase in optical absorption, generation of photoluminescence, as well as mechanical bending. On the other hand, the identical substrates coated with Indium-tin-oxide (ITO), which is a typical material for transparent electrodes in photovoltaics, exhibit significantly higher resistance to the modifications by protons while ITO structural and electronic properties remain unchanged. The experimental results are discussed considering a potential application of these materials for missions in space.

Abstract One of the reasons chalcogenide-based photovoltaic solar cells (SC) do not yet meet the expected high-power conversion efficiencies is a lack of understanding of their electronic structure, and particularly the nature of the point defects in the absorber materials. We show that the density of states of the characteristic features of the electronic structure, such as band edges and energy distribution of defects, can be obtained experimentally by energy-resolved electrochemical impedance spectroscopy (ER-EIS) in a technically simple and quick way. The ER-EIS data correlate well with theoretical density functional theory calculations. The ER-EIS reveals that Bi2S3, has only shallow defects near the conduction band minimum (CBM). In Sb2S3, ER-EIS also shows deep defect states, which can be the cause of the low electrical conductivity of Sb2S3 and lower than theoretically possible power conversion efficiency of Sb2S3-based SC. A dominant sulphur vacancy defect was identified in Bi- and Sb-chalcogenides. In the (Sb x Bi(1−x))2S3 ternary alloy series, a gradual transformation of CBM and defect states in the band gap was observed. Notably, a 1:9 ratio of Bi:Sb cations already transforms the deep sulphur defects into shallow ones while keeping the band edges similar to those of the pristine Sb2S3. It can provide a novel strategy for healing the deep defect states in Sb2S3, a crucial step for boosting solar cell performance.

Abstract The microcrystalline hydrogenated silicon has one clear advantage – stability against light-induced changes – but rather complicated growth and microstructure. As a result there are many problems and specific features of transport in microcrystalline silicon. These features – like inhomogeneity, anisotropy, influence of substrate and thickness dependence are discussed in detail.

Charge transport in microcrystalline silicon is strongly influenced by its heterogeneous microstructure composed of crystalline grains and amorphous tissue. An even bigger effect on transport is their arrangement in grain aggregates or possibly columns, separated by grain boundaries, causing transport anisotropy and/or depth profile of transport properties. We review special experimental methods developed to study the resulting transport features: local electronic studies by combined atomic force microscopy, anisotropy of conductivity and diffusion length and also their thickness dependence. A simple model based on the concept of changes of transport path for description of the observed phenomena is reviewed and its consequences for charge collection in microcrystalline based solar cells are discussed.

Organic-based photovoltaic devices emerged as a complementary technology to silicon solar cells with specific advantages in terms of cost, ease of deployment, semi-transparency, and performance under low and diffuse light conditions. In this work, thin-film boron-doped diamond (B:NCD) electrodes are employed for their useful op-tical, electronic, and chemical properties, as well as stability and environmental safety. A set of oligothiophene perylene diimide (nT-PDI) donor-acceptor chromophores is designed and synthesized in order to investigate the influence of the oligothiophene spacer length when the nT-PDI molecule is attached to a B:NCD electrode. The chromophores are anchored to the diamond surface via diazonium grafting followed by Sonogashira cross -coupling. X-ray photoelectron spectroscopy shows that the surface coverage decreases with increasing oligo-thiophene length. Density functional theory (DFT/TDDFT) calculations reveal the upright nT-PDI orientation and the most efficient photogenerated charge separation and injection to diamond for elongated oligothiophene chains (8T-PDI). Yet, the maximum photovoltage is obtained for an intermediate oligothiophene length (3T-PDI), providing an optimum between decreasing transport efficiency and increasing efficiency of charge separation and reduced recombination with increasing oligothiophene length. Holes transferred from nT-PDI to diamond persist there even after the illumination is switched off. Such features may be beneficial for application in solar cells. The authors thank Hasselt University, the Research Foundation Flanders (FWO Vlaanderen), and the European Regional Development Fund project CZ.02.1.01/0.0/0.0/15_003/0000464 (CAP) for financial support. J. Raymakers thanks the FWO for his PhD fellowship. This work was also supported by The Ministry of Education, Youth and Sports through the e-INFRA CZ (ID:90140) project, the Large Research Infrastructures IT4Innovations, and Czech Nano Lab. The authors also thank Dr. Jasper Deckers for his valuable assistance at the revision stage.