Organic and a-Si Solar Cells for Energy Harvesting

In the last decades, lots of research have been performed with the purpose of obtaining solar cells with improved properties, and for extending their use in energy harvesting (EH) applications. In this paper, we designed and simulated two different solar cells, one based on organic materials and the other on amorphous silicon (a-Si), each in two different light intensity conditions (corresponding to outdoor and indoor functioning, respectively). We compared their performance in terms of the main characteristics and parameters and concluded that the organic solar cells have better results than the a-Si ones and have promising perspectives for being used in EH applications, in low light or indoor situations. As compared to other literature research, our paper proposes a careful choice of materials and parameters, for the PEDOT:PSS-based organic solar cell, to improve its performance; moreover, the use of the AFORS-HET software enabled us to perform a detailed comparative analysis of two different structures of solar cells, at two different illumination levels (to estimate the behaviour both in outdoor and indoor conditions), that could be followed by an experimental validation and testing of a real structure.

I. Introduction

Since decades, scientists have tried to find the best solutions to use the ambient energy, as a cleaner and renewable alternative to fossil fuels, that release harmful greenhouse gases and their resources could be exhausted in time. In this context, an efficient approach is the so-called energy harvesting (EH), a process that takes the ambient energy (that can have many forms: thermal energy, solar energy, wind energy, kinetic energy etc.) and converts it into electrical power that can be used for various low-energy electronic devices, working in indoor or low-light conditions, such as for prolonging the battery life of mobile phones, tablet PCs, for wearable electronics, wireless sensor networks etc., in offices, smart buildings and in various other areas [1]–[3]. One of the most efficient solutions for EH is the solar cell. These devices can be classified in two main types: crystalline (either monocrystalline or polycrystalline) and thin-film cells. The most used crystalline solar cells are based on silicon, whereas thin-film solar cells can have, as materials for the active layer, different organic materials, amorphous silicon (a-Si), perovskites, copper indium gallium selenide (CIGS), cadmium telluride (CdTe), gallium arsenide (GaAs), various dyes (in dye-sensitized solar cells) etc. To increase the efficiency, multi-junction (also named tandem) solar cells were also proposed, where several different cells are connected [3]–[6].