OPV Polymers

Organic solar cells, also known as organic photovoltaics (OPVs), have become widely recognized for their many promising qualities. This page introduces the topic of OPVs, how they work and their development.

Whilst the majority of commercial solar cells are currently made using crystalline silicon (c-Si), thin-film alternatives have the potential to be cheaper, flexible, and more straightforward to produce. These technologies can be classified as second-generation cells (e.g. cadmium telluride (CdTe)), or third-generation (e.g. perovskite solar cells).

A solar cell is a device that converts light into electricity via the ‘photovoltaic effect’. They are also commonly called ‘photovoltaic cells’ after this phenomenon, and also to differentiate them from solar thermal devices. The photovoltaic effect is a process that occurs in some semiconducting materials, such as silicon.

While a large part of research into the bulk heterojunction morphology of organic solar cells focuses on component choice,1 the morphology is also tuned by a host of processing conditions. Recently, Singh et al.2 published work into optimising three of these conditions; the molar mass ratio of the donor:acceptor blend, the annealing temperature of the active layer and the cathode buffer layer choice.

Typically, organic photovoltaics (OPVs) are manufactured in the form of a bulk heterojunction (BHJ) cell, where the active layer consists of a blend of donor and acceptor materials with various interfacial layers and electrodes (seen in Figure 1). For OPVs to be commercially competitive with existing solar technologies, a ’10/10’ target must be reached, which refers to a 10% power conversion efficiency (PCE) and 10-year lifetime.

HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) are fundamental concepts in molecular orbital theory. HOMO and LUMO are known as the "frontier molecular orbitals" because they are the highest occupied and lowest unoccupied molecular orbitals, respectively.

Polymer-fullerene bulk heterojunction (BHJ) solar cells are based on blends of semiconducting polymers and fullerene derivatives, such as PCBM. It is described as a bulk heterojunction as it involves a blend of two materials with differing energy band gaps, forming a dispersed, interpenetrating network.