Abstract
In this thesis, I focus on the fabrication and characterization of solution-processed small molecule organic solar cells (SMOSCs) and organic-inorganic hybrid solar cells. In the first chapter, I briefly review the development of modern photovoltaics including SMOSCs, polymer solar cells, silicon/organic organic-inorganic hybrid solar cells and perovskite solar cells. In the second chapter, the operation principles and characteristics of organic and organic-inorganic hybrid solar cells are described, followed by the details of device structures, materials analyses, device fabrications and characteristics measurements. In the third chapter of the thesis, a series of acceptor-acceptor-donor-acceptor-acceptor (A-A-D-A-A) symmetrical small molecules are studied as donor material for solution-processed SMOSCs. Various fabrication methods, device structures and acceptor materials are used to optimize the cell performance. Among all compounds, JW2 gives the highest power conversion efficiency (PCE) of 1.7 %, with an open circuit voltage (Voc) of 0.85 V, a short circuit current density (Jsc) of 5.26 mA/cm2, and a fill factor (F.F.) of 0.39. In the fourth chapter, we fabricate planar-type organic-inorganic hybrid solar cells based on single crystalline silicon covered by organic hole transporting material poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). A simple surface passivation method: Ultraviolet (UV)-ozone treatment is demonstrated. The effects of Si/PEDOT:PSS interfaces on device performances are further studied. In the second part of this chapter, the dielectric material-metal-dielectric material (DMD) structures as transparent electrodes are applied to the planar-type organic-inorganic solar cells. Finally, pyramid structures are tested and investigated under optical microscope and scanning electron microscope. In the fifth chapter of the thesis, blade-coated and spin-coated perovskite films are first fabricated. High efficiency solution-processed perovskite solar cells with an optimized annealing time and electron transporting layer thickness deliver a PCE of 11.7 %, with Voc of 0.87 V, a Jsc of 20.74 mA/cm2, a F.F. of 0.65. The PCE is further improved to 13.8 % by fine tuning of the material composition in the perovskite absorbing layers. In the last part of this section, several transporting layers are inserted into the device structures and Indium Tin Oxide (ITO)-free perovskite solar cells are successfully fabricated.