Lateral-tandem organic solar cells
Organic Solar Cells (OSCs) are a promising candidate to solve the energy issues of the current world due to its growing population and their needs. OSCs generate electric current by generating carriers using organic semiconductors either in their crystal form or in thin films. Such organic semiconductor devices have various advantages such as low cost, flexibility, small weight, and printability. Organic semiconductors with very high mobility for carriers are already reported in previous studies. C8-BTBT and PTCDI-C8 are well known organic materials acting as electron donor and acceptor, respectively, and showing high mobilities for holes and electrons, respectively. This high mobility of carriers paved the way for the lateral organic solar cell operation in which the carriers generated are collected laterally. Thus, unlimited layers can be stacked to absorb the entire wavelength of the solar spectrum. This can overcome the thickness limitation of conventional vertical cells in which the thickness is limited to a few nanometers. Thus, the lateral cells can increase the efficiency of organic solar cells. But the photocurrent generated by these lateral cells was small compared to the typical vertical cell. It is due to the low carrier generation efficiency caused by the long insulating chains between C8-BTBT and PTCDI-C8 molecules.
To overcome this low photocurrent generation in lateral cells, organic materials having a high ability to absorb sunlight such as DBP are introduced between the C8-BTBT and PTCDI-C8. Thus, this light absorber acts as carrier generating layer and C8-BTBT and PTCDI-C8 act as carriers transporting films. A lateral cell with only a carrier-transporting layer (C8-BTBT/PTCDI-C8) (Fig. a) exhibited significantly low photocurrent density. The cells having carrier-generating and transporting layers (Fig. b) showed a larger photocurrent compared to the C8-BTBT/PTCDI-C8 lateral cells. Further, the photocurrent has drastically increased by increasing the number of carriers generating and transporting layers by stacking one over the other. Hence, the lateral tandem cell in which the number of cells is stacked one above the other was successfully operated.
The advantage of the lateral tandem cell (Fig. c) is that a single device can have several cells stacked one over the other so that the entire sunlight that falls on it can be converted to electric current. Hence a major part of the solar spectrum can be effectively converted to the photocurrent by using such solar panels. Since the organic materials are cheap, the lateral organic solar cells can be a boon to the common people. Thus, the lateral tandem cells can be the future solar cell.
Bibliographic information of awarded paper
- Title: Lateral-tandem organic photovoltaic cells with carrier transport and generation layers
- Authors: Palassery Ithikkal Jaseela, Yusuke Yabara, Uto Shoko, Seiichiro Izawa, Masahiro Hiramoto
- Journal Title: Applied Physics Express 14, 101003
- Publication Year: 2021
- DOI: https://doi.org/10.35848/1882-0786/ac28e6
Department of Functional Molecular Science Palassery Ithikkal Jaseela