Nanostructured Hybrid Solar Cells Research Articles

Desirable TiO2 compact films for nanostructured hybrid solar cells

ABSTRACTTwo different TiO2 compact films, fabricated by sol-gel spin-coating (SC) and spray-pyrolysis (SP) processes, were employed as an electron transport layer (ETL) to the nanostructured hybrid perovskite solar cells (PSCs), and they were comprehensively investigated through the various characterisation approaches using electrochemical and physicochemical approaches. With cyclic voltammetry and XPS results, the absence of pinholes on the SP-TiO2 compact films was indicated, and AFM and SEM results confirmed the SP-TiO2 compact films had lower surface roughness and more compact particle connectivity, offering a decent interface between the perovskite active layer and the adjacent TiO2 films. The performance of the SP-PSCs using the SP-TiO2 compact films was 7.06%, which was 3 times higher than that of the SC-PSCs. Voc decay measurement also confirmed that such pinhole-free and improved film interfaces of SP-TiO2 compact films contributed to elongating electron lifetime in PSCs by the enhanced hole blocking effect of the SP-TiO2 compact films.

Relation between Morphology and Recombination Kinetics in Nanostructured Hybrid Solar Cells

Systematic performance improvement of excitonic solar cells hinges on thorough knowledge of their main loss mechanisms. Accordingly, the study of recombination kinetics is indispensable, enabling to identify and quantify what is considered the most important loss pathway for such devices. In contrast to the advances made in controlling the morphology of organic bulk heterojunction solar cells, it remains challenging to establish a robust correlation between morphology and recombination kinetics. Most obvious culprits are the rather disordered nature of most heterojunctions and the absence of phase purity. In that respect, hybrid solar cells based on ZnO nanorod arrays and poly(3-hexylthiophene) can offer a convenient means to study recombination, as their morphology is easier to control and to quantify. Therefore, tunability of bulk and interfacial morphology of such solar cells is utilized in this work to evidence a direct relation between morphology, recombination kinetics and device performance.

Solution-processed, nanostructured hybrid solar cells with broad spectral sensitivity and stability

Hybrid organic-inorganic solar cells, as an alternative to all-organic solar cells, have received significant attention for their potential advantages in combining the solution-processability and versatility of organic materials with high charge mobility and environmental stability of inorganic semiconductors. Here we report efficient and air-stable hybrid organic-inorganic solar cells with broad spectral sensitivity based on a low-gap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and spherical CdSe nanoparticles. The solvents used for depositing the hybrid PCPDTBT:CdSe active layer were shown to strongly influence the film morphology, and subsequently the photovoltaic performance of the resulted solar cells. Appropriate post-deposition annealing of the hybrid film was also shown to improve the solar cell efficiency. The inclusion of a thin ZnO nanoparticle layer between the active layer and the metal cathode leads to a significant increase in device efficiency especially at long wavelengths, due to a combination of optical and electronic effects including more optimal light absorption in the active layer and elimination of unwanted hole leakage into the cathode. Overall, maximum power conversion efficiencies up to 3.7 ± 0.2% and spectral sensitivity extending above 800 nm were achieved in such PCPDTBT:CdSe nanosphere hybrid solar cells. Furthermore, the devices with a ZnO nanoparticle layer retained ∼70% of the original efficiency after storage under ambient laboratory conditions for over 60 days without any encapsulation.

Influence of Interface Morphology onto the Photovoltaic Properties of Nanopatterned ZnO/Poly(3-hexylthiophene) Hybrid Solar Cells. An Impedance Spectroscopy Study

This paper focuses on the characterization of the ZnO/poly(3-hexylthiophene) (P3HT) interfaces in nanostructured hybrid solar cells, aiming to elucidate the relationship between thermal treatment, local morphology, and device performance. An equivalent impedimetric model for the device is proposed, allowing us to extract information about the ZnO/P3HT interface morphology and its impact on the photovoltaic properties by comparing devices with and without nanopatterning. It is found that the influence of thermal treatment on performance lies solely in the interface, resulting from a different interfacial morphology of P3HT depending on which crystal direction of ZnO is present.

Nanostructured Organic and Hybrid Solar Cells

This Progress Report highlights recent developments in nanostructured organic and hybrid solar cells. The authors discuss novel approaches to control the film morphology in fully organic solar cells and the design of nanostructured hybrid solar cells. The motivation and recent results concerning fabrication and effects on device physics are emphasized. The aim of this review is not to give a summary of all recent results in organic and hybrid solar cells, but rather to focus on the fabrication, device physics, and light trapping properties of nanostructured organic and hybrid devices.

Improved Efficiency in Poly(3-hexylthiophene)/Zinc Oxide Solar Cells via Lithium Incorporation

The efficiency of poly(3-hexylthiophene)/zinc oxide planar heterojunction solar cells is on average raised by a factor of 2.9 by incorporating lithium during the sol−gel processing of the metal oxide layer. Studies performed on over 300 diodes show systematic increases in both open-circuit voltage (Voc) and short-circuit current (Jsc) up to an optimum Li concentration between 15 and 20 atom %. Compared to pure ZnO devices, the incorporation of lithium improves the Voc and Jsc by an average of 42 and 90%, respectively. For the best device, the efficiency increases by a factor of 7.5, yielding a power conversion efficiency of 0.44%, which is approaching the efficiency of the state-of-the-art nanostructured hybrid solar cells. Enhancements in Voc are attributed to a larger donor−acceptor energy band edge offset due to a rigid shift of Zn1−xLixO energy levels toward to the vacuum level with Li incorporation. Jsc improvements arise from a higher surface roughness with lithium incorporation and from better P3HT...

Nanostructured Hybrid Solar Cells Based on Self-Assembled Mesoporous Titania Thin Films

Nanocrystalline mesostructured porous titania thin films with optimized coating and thermal curing conditions have been prepared for the first time using spin-coating deposition technique. The X-ray diffraction (XRD) and the grazing incidence small-angle X-ray scattering (GI-SAXS) measurements revealed that the crystallization and diffuse sintering of amorphous TiO2 into anatase are simultaneously starting between 400 and 500 °C curing temperature, leading to a gridlike open-pore-shape transformation. The environmental ellipsometric porosimetry (EEP) measurements show that the 550 °C-cured TiO2 films exhibit a high porous volume (0.30 cm3 g-1), a large surface area (172 m2 cm-3), and a Young modulus of 1.05 GPa. All solid-state dye-sensitized solar cells (DSSC) based on nanocrystalline mesostructured TiO2 films and poly(3-octylthiophene) as hole conductor allow reproducible achievement of energy conversion efficiencies of about 0.52%. These values, obtained with thin TiO2 films (250 nm), are very promising.