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In the last few years, perovskite-based solar cells have seen rapid improvements of their power conversion efficiencies (PCE) that have already reached silicon cell values. The commercial use of perovskite cell technology remains, however, a challenge due to durability issues. In fact, perovskite films when exposed to moisture and oxygen undergo degradation within a couple of hours or days. In order to address these problems, several strategies have been developed in recent years, including surface passivation and coating. Herein, we analyze and compare two perovskite stability improvement approaches, each aimed at the reduction of the oxygen diffusion, one by adding chlorine to perovskite precursors in order to block iodine vacancy sites, and the other by coating the perovskite layers with protective Al2O3 films using Atomic Layer Deposition (ALD). The study provides an experimental verification of the degradation mechanism linking it to oxygen diffusion into the perovskite films. As shown by X-ray photoelectron spectroscopy (XPS) analysis, the addition of chlorine into the iodine-based perovskite film slows down the oxygen diffusion, while X-ray diffraction (XRD) measurements show improved stability of such iodide perovskite with chlorine addition. Characteristic times for oxygen diffusion into subsurface region as well as for degradation process of film volume are provided and discussed. XRD measurements are also used to show that an additional significant stability improvement can also be achieved when the films are coated with a protective ALD Al2O3 layer.

The plasmonic photovoltaic effect of mediation by surface plasmons in the harvesting of solar light energy in metallically surface-nanomodified photodiodes or solar cells is described in the microscopic manner. The experimentally observed increase in the efficiency of the photo-effect due to plasmons is explained by the competition between two opposing effects: that of the field concentration in plasmon oscillations and that of the admittance of indirect inter-band transitions in a semiconductor substrate induced by dipole coupling to plasmons at the nanoscale without translational invariance. The former effect favors larger metallic nanocomponents, whereas the latter effect prefers smaller nanocomponents. Both factors are quantitatively addressed within the quantum Fermi golden rule scheme, which allows for the size analysis of the plasmon effect and for its optimization. Experimental verification of the theoretical predictions is presented, including the demonstration of the proximity and size effect in double-layer photo-active substrate. The experiment reveals that the plasmon effect is still present if metallic nanoparticles are separated from substrate by the distance of order of 1 μm.

The theoretical approach towards improving the photovoltaic response of n-ZnO/p-Si heterojunctions proposed by Knutsen et al. [Phys. Status Solidi A 210 (2013) 585–588] has been experimentally tested. AZO/n-Zn(1−x)MgxO layers were deposited at 160 °C on p-Si substrates by atomic layer deposition (ALD) with magnesium concentration in the 0–4 at% range. The examined devices showed a reduction of the conduction band offset from (0.63±0.03) eV to (0.48±0.03) eV. This decrease leads to a diminishing impact of recombination centers at the interface between zinc oxide based layers and silicon substrate, when the Mg content is below ~1.6 at%. In this range, the overall photovoltaic efficiency increased from ~3.7% to ~6.0%. As a next step, we tested solar cells with similar magnesium concentration in the Zn(1−x)MgxO layer, but deposited at 300 °C. Due to the higher deposition temperature, a further 1.1% increase in efficiency has been obtained. So far, this is the highest reported efficiency for a ZnO/Si heterojunction grown by ALD method, thus experimentally confirming the validity of the approache s here studied for raising the efficiency of heterojunctions solar cells based on n-ZnO/p-Si, while significantly reducing the fabrication complexity respect to conventional Si based devices as emphasized by Hussain et al. [Sol. Energy Mater. Sol. Cells 139 (2015) 95–100].

In this paper, cheap and efficient photovoltaic cells based on ZnO/Si heterostructure are discussed. These cells contain zinc oxide nanorods (ZnONR) grown by a low temperature hydrothermal method on a p-type silicon surface. The hydrothermal method applied in the present work uses cheap precursors and allows reproducible and controllable growth of 3D systems. As-grown ZnONR on Si surface are uniformly covered by a zinc oxide (ZnO) layer followed by an aluminum doped zinc oxide (AZO) layer. The latter is deposited on top of the cell as transparent conductive oxide (TCO). Both zinc oxide and aluminum doped zinc oxide layers are grown by a low temperature atomic layer deposition (LT ALD) method. Thickness of ZnO layers is optimized to increase significantly the light-trapping effect and thus the photovoltaic (PV) response. We evaluate impact of ZnO thickness on the PV devices operation. It is found that PV efficiency increases when thickness of the ZnO layer changes from 50 nm to 500 nm. The best response of solar cells is achieved for a sample containing ZnO layer with a thickness equal to 500 nm. The overall photovoltaic response is 10.9% and can be further improved by contact and Si layer optimization.