Building an Organic Solar Cell: Fundamental Procedures for Device Fabrication

Abstract

This laboratory experiment is designed to train undergraduate students in the fundamental steps followed in engineering solution-processed organic solar cells and to offer insight on the operating principles of said device. Bulk heterojunction (BHJ) organic solar cells represent a photovoltaic architecture which has attracted a lot of attention due to its promising properties; moreover, this architecture, due to its low cost and potential, is continuously being investigated and improved. This paper is intended as a useful step-by-step guide for students and researchers to learn how to construct such a device. Another primary objective of this article is to highlight the importance of optimizing device performance through enhancing the optical, electrical, and morphological properties of the materials selected as building blocks. Once a completed organic solar cell is made, students will also learn how to investigate and assess its performance through a series of spectroscopic, electrical, and morphological characterization measurements.Energies 2019, 12, 2188 2 of 23 an electron transport layer or ETL (e.g., calcium) and a cathode (e.g., aluminum or silver). The feature that differentiates BHJ OSCs from the previously-developed bi-layer OSCs is the way that the electron donor and the electron acceptor are deposited. In the bi-layer structure the photoactive layer is structured by first depositing the donor polymer and then depositing the acceptor material. The active layer is "sandwiched" between the ETL and HTL. However, in a BHJ OSC, the electron donor and the electron acceptor materials are first mixed in a blend (diluted in the same solvent) before being deposited between the ETL and HTL.After the description of the fabrication process, the device characterization is also presented. Firstly, the photovoltaic performance was evaluated by measuring the current density-voltage (J-V) using the solar simulator, then external quantum efficiency (EQE) measurements were taken to re-confirm the J-V calculated parameters. The optical properties were assessed with absorbance measurement of the AL via UV-Vis spectroscopy. The morphology and roughness of the HTL and AL were also investigated using AFM. Lastly, charge carrier mobility measurements were carried out, namely hole and electron mobilities of the transporting layers. This part of the experiment aims to teach students and dispense the characterization methods implemented to assess the overall performance of an organic solar cell and to evaluate/realize the result of each measurement.The present manuscript presents in detail the process followed throughout the fabrication of a bulk heterojunction organic solar cell. The role of each material, the criteria with which each compound was chosen, what measurements were carried out to assess each material's suitability, and the overall electrical and optical performance of the completed device are presented. In the experiment outlined in this manuscript, students (a) followed the fabrication process step by step, becomi...

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