Fabrication and study of sol-gel ZnO films for use in Si-based heterojunction photovoltaic devices

This paper considers the use of zinc oxide thin films prepared via the sol-gel route as an n-type layer in heterojunction ZnO/Si solar cells. The ZnO films were prepared via a simple spin-coating technique using zinc acetate dihydrate as a zinc precursor, isopropanol as a solvent and monoethanolamine as a stabilizing agent. Optical, structural and morphological properties of ZnO were investigated for thin films grown from sol-gel solutions with different concentrations both on glass and silicon substrates. As such, a distribution of crystallite sizes and surface topology parameters corresponding to various zinc acetate dihydrate concentrations were obtained to elucidate optimal film deposition conditions. Correlation between thin film morphology and structural characteristics of ZnO thin films was made based on atomic-force microscopy studies. Finally, our results on fabrication, characterization and simulation of ZnO/Si heterojunctions for use as photovoltaic devices are presented. Although noticeable rectifying and photovoltaic properties were observed for Al/Si/ZnO/Ti/Au devices, there appears to exist a considerable room for device improvement with simulation studies suggesting that efficiencies of the order of 24% may be obtained for devices with optimal silicon wafer passivation, i.e. with lifetimes of the order of 1000 μs

Characterization of a Heterojunction Silicon Solar Cell by Means of Impedance Spectroscopy

Impedance spectroscopy provides relevant knowledge on the recombination and extraction of photogenerated charge carriers in various types of photovoltaic devices. In particular, this method is of great benefit to the study of crystalline silicon (c-Si)-based solar cells, a market-dominating commercial technology, for example, in terms of the comparison of various types of c-Si devices. This study investigates the dark and light electrophysical characteristics of a heterojunction silicon solar cell fabricated using plasma-enhanced chemical vapor deposition. The measurements are performed at various applied biases, enabling the determination of complex resistance, characteristic time, capacitive response and impurity concentration within the semiconductor junction and to correlate them with the device performance. In addition, the impedance spectra of the studied cell were investigated as a function of temperature. Studies of the frequency and temperature dependences of capacitance do not reveal a significant presence of thermally activated centers of free carrier capture, concomitant with a very small value of the activation energy extracted from an Arrhenius-type analysis. This leads to a conclusion that these centers are likely not impactful on the device operation and efficiency

Development of a mobile independent solar power plant based on solid-state heterojunction photocells for agricultural purposes

Mathematical simulation of temperature distribution on double-sided solar cells has been carried out. Differences in the configuration of photoelectric converters prove to solely amount to the fact that a double-sided solar cell has a more efficient heat sink at the rear side. Furthermore double-sided solar cells exhibit higher power conversion performance. Calculations confirm the correctness of giving preference to double-sided solar cells which is of great importance for the photoelectric converter design developed by us. Analysis of market-available photovoltaic technologies of solar energy to electric power conversion has led to the development of a photovoltaic converter on the basis of double-sided silicon heterojunction solar cells. The configuration developed is a moving platform having a photovoltaic cell array mounted on it and a light flux collector. A double-axis tracking system has been developed for the general case of planar attachment of solar cell modules. A 350 mm stroke drive provides for movement in the north-south direction and a 450 mm stroke drive, in the east-west direction. The task has been outlined to find the required arm for providing symmetrical positioning at the maximum rotation angle about the axis. As a result, technical solutions have been developed for the north-south and the east-west directions. Furthermore a schematic wiring diagram has been designed to implement the preset solar tracking system algorithm. The system is also fitted with a GPS/GLONASS module for system precision positioning and time synchronization