The effect of donor layer thickness on the power conversion efficiency of organic photovoltaic devices fabricated with a double small-molecular layer

Abstract

In organic photovoltaic (OPV) devices fabricated with a double small-molecular layer, the power conversion efficiency strongly depends on the thickness of the organic donor layer (here, copper phthalocyanine). In other words, the power conversion efficiency increases with the donor layer thickness up to a specific thickness ( approximately 12.7 nm) and then decreases beyond that thickness. This trend is associated with the light absorption and carrier transport resistance of the small-molecular donor layer, both of which strongly depend on the layer thickness. Experimental and calculated results showed that the short-circuit current due to light absorption increased with the donor layer thickness, while that due to current through the donor layer decreased with 1/R. Since the total short-circuit current is the product of the light absorption current and current through the donor layer, there is a trade-off, and the maximum power conversion efficiency occurs at a specific organic donor layer thickness (e.g. approximately 12.7 nm in this experiment).

Effect of NiOx thin layer fabricated by oxygen-plasma treatment on polymer photovoltaic cell

“…Many researchers have particularly sought to improve the performance of polymer PV cells because their power conversion efficiency (PCE) has not approached that of thin-inorganic solar cells enabling them to become more competitive in the market. The polymer PV cell structure consists of diverse layers with individual functions [6][7][8][9][10]. The PCE of polymer PV cell is generally determined by a multitude of factors affecting holeelectron pair generation, including light absorption in the donor material and electron-acceptor material, transport of lightgenerated excitons from both layers (donor and acceptor layers) to the donor-acceptor interface, and the efficiency of exciton separation into electron-hole pairs at the donor-acceptor interface.…”

“…The PCE of polymer PV cell is generally determined by a multitude of factors affecting holeelectron pair generation, including light absorption in the donor material and electron-acceptor material, transport of lightgenerated excitons from both layers (donor and acceptor layers) to the donor-acceptor interface, and the efficiency of exciton separation into electron-hole pairs at the donor-acceptor interface. Moreover, the transportation of charge carriers across the active layer to electrodes and the condition of polymer-metal interface also play a significant role in the performance of polymer PV cell [9]. Many approaches have been found to improve the performance of PV cells by modifying their structure to achieve effective and enhanced injection of carriers.…”

Effect of Metal-Reflection and Surface-Roughness Properties on Power-Conversion Efficiency for Polymer Photovoltaic Cells

“…Recently, organic photovoltaic (OPV) cells have attracted attention as a renewable, sustainable source of electricity, because they are a clean energy source, have a low fabrication cost, and can be processed on a flexible substrate. − In particular, many researchers have sought to improve the photovoltaic (PV) cell performances such as the power conversion efficiency (PCE). − The PCE of an OPV cell is generally determined by a multitude of factors, including the light absorption in the electron-donor material, light absorption in the electron-acceptor material, transport of light-generated excitons from both layers to the donor−acceptor interface, efficiency of the hole/exciton separation into electron−hole pairs at the interface, transport of holes across the donor layer to the anode, transport of electrons across the acceptor layer to the cathode, quality of the contact between the donor layer and the anode, and quality of the contact between the acceptor layer and the cathode. Thus, many researchers have made efforts to improve the PCE of OPV cells by modifying the donor, acceptor, blocking material, and PV cell structure. − However, most of researchers have not investigated the effect of the metal optical property on the PCE. Our study investigates how the reflectivity, resistance, and surface roughness of a metal cathode influence the performance on the polymer PV cells such as short-circuit current ( J sc ), open-circuit voltage ( V oc ), fill factor (FF), and PCE.…”

Polymer photovoltaic cell embedded with p-type single walled carbon nanotubes fabricated by spray process

“…Therefore, to understand why the SWCNT concentration (or SWCNT spray frequency) in polymer PV cells mainly affects J sc , we investigated the dependences of light absorption, shunt resistance, and series resistance on the SWCNT spray frequency. It was reported that J sc values for organic PV cells are generally affected by light absorption and carrier (hole and electron) transport resistance, which affects PCE inversely [14]. Thus, to determine whether the dependence of J sc on the SWCNT spray frequency is mainly associated with the increase of the light absorption via SWCNTs, the light absorption was measured as a function of the SWCNT spray frequency, as shown in figure 6.…”

“…Thus, many researchers have put their effort into enhancing the PCE of polymer PV cells by developing a wide energy bandgap and high carrier mobility polymer, tandem, novel PV cell structure, and the plasmon effect etc [6][7][8][9][10]. The polymer PV cell structure consists of diverse layers with individual functions [11][12][13][14][15]. In addition, carbon nanotubes (CNTs) are enormously attractive because they have demonstrated extremely fast carrier mobility [16], flexibility, environmental 1 Author to whom any correspondence should be addressed.…”