Levelised cost of electricity for organic photovoltaics

The success of organic photovoltaics (OPVs) as a future energy source is entirely dependent on the cost of the electricity produced by the modules. This study provides the first commercial scale levelised cost of electricity (LCOE) estimates for OPVs by integrating OPV-specific measured and calculated data into the estimates. The impacts of physical and financial variables are also investigated. The study shows that OPVs will become equivalently priced with current conventional solar technologies when efficiencies of 2% and lifetimes of three years are achieved. At efficiencies of 5% and lifetimes of 3–5 years the LCOE for OPVs will be competitive with that of current coal-based electricity generation

Enhanced regeneration of degraded polymer solar cells by thermal annealing

The degradation and thermal regeneration of poly(3-hexylethiophene) (P3HT):[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) and P3HT:indene-C₆₀ bisadduct (ICBA) polymer solar cells, with Ca/Al and Ca/Ag cathodes and indium tin oxide/poly(ethylene-dioxythiophene):polystyrene sulfonate anode have been investigated. Degradation occurs via a combination of three primary pathways: (1) cathodic oxidation, (2) active layer phase segregation, and (3) anodic diffusion. Fully degraded devices were subjected to thermal annealing under inert atmosphere. Degraded solar cells possessing Ca/Ag electrodes were observed to regenerate their performance, whereas solar cells having Ca/Al electrodes exhibited no significant regeneration of device characteristics after thermal annealing. Moreover, the solar cells with a P3HT:ICBA active layer exhibited enhanced regeneration compared to P3HT:PCBM active layer devices as a result of reduced changes to the active layer morphology. Devices combining a Ca/Ag cathode and P3HT:ICBA active layer demonstrated ∼50% performance restoration over several degradation/regeneration cycles

Comparing the degradation of organic photovoltaic devices under ISOS testing protocols

In order for OPV devices to transition from the laboratory to the industrial scale, accurate measurements of device operating stability and lifetime are crucial. This paper compares the degradation of ITO/PEDOT: PSS/P3HT:ICBA/Ca/Al and ITO/MoO3/P3HT:ICBA/Ca/Al devices using the three main ISOS standard testing protocols: (a) ISOS-D-1, (b) ISOS-O-1 and (c) ISOS-L-1. We show that: (1) ITO/MoO3/P3HT:ICBA/Ca/Al devices are more stable than their PEDOT counterparts under the ISOS-D-1 protocol, as has been reported previously. (2) Under the ISOS-O-1 protocol, unencapsulated MoO3 based devices are more stable than the equivalent PEDOT device but, when encapsulated, the degradation rates of the MoO3 and PEDOT devices are the same. (3) By contrast, when measured under the ISOS-L protocol, the MoO3 based devices are either equivalent to (unencapsulated devices) or, indeed, actually degrade faster (encapsulated devices) that their PEDOT counterparts. We demonstrate that these differences arise from the dominant degradation mode changing under the different protocols. As such, this paper highlights that the choice of testing protocol significantly influences the reported stability of OPV devices. In particular, the ISOS-D and ISOS-L protocols do not necessary reflect OPV device performance under actual operating conditions and thus stability measurements using these protocols should be treated with caution

Comparative degradation and regeneration of polymer solar cells with different cathodes

A comparative degradation study of solar cells based on a bulk-heterojunction (BHJ) blend of poly(3-hexylethiophene) (P3HT) and phenyl [6,6] C₆₁ butyric acid methyl ester (PCBM) with two different cathodes is reported. Poly(ethylene-dioxythiphene):poly(styrene sulfonate) (PEDOT:PSS) coated ITO electrodes were used as the anode, whereas Ca/Al and Ca/Ag electrodes were used as cathodes. Fully degraded devices were subjected to thermal annealing under inert atmosphere. The performance of degraded solar cells with a Ca/Al cathode exhibited no improvement after treatment. However the solar cells with a Ca/Ag cathode exhibited a considerable recovery in their performance following annealing under a nitrogen atmosphere. Indeed, these solar cells could be subjected to many degradation and regeneration cycles. Current density–voltage (J-V) characteristics and X-ray photoelectron spectroscopy (XPS) studies show that this behavior arises from the complex chemical thermodynamics of the reactions that can occur at the cathode/active layer interface. In particular, the recovery of device performance for solar cells with a Ca/Ag cathode is due to the reversible oxidation of Ag upon thermal annealing

Solution processable interface materials for nanoparticulate organic photovoltaic devices

Nanoparticulate zinc oxide can be prepared at low temperatures from solution processable zinc acetylacetonate. The use of this material as a cathode interfacial layer in nanoparticulate organic photovoltaic devices results in comparable performances to those based on reactive calcium layers. Importantly, the enhanced degradation stability and full solution processability make zinc oxide a more desirable material for the fabrication of large area printed devices