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Organic Photovoltaics

A variety of experimental and theoretical research is carried out in Durham to reveal the relationships between the structure of organic photovoltaic devices and their performance. Such devices promise to dramatically reduce the cost of renewable energy due to their scalable manufacturing processes.

Kinetic Monte Carlo modelling of Charge Transport in Organic Semiconductors and Photovoltaics

We develop and use Monte Carlo models to investigate the relationship between the energetic and morphological structure of a device and the performance of devices, and photovoltaics in particular. In particular this allows us to make links between properties of organic materials on the nano-scale to bulk, measureable properties. Across shows one example of this, where we plot the distribution of current emerging from a polymer film. It can be seen that the current is extremely heterogeneous as a result of energetic disorder in the polymer.

Recently we have extended this work to use course-grained models to simulate how conjugated polymers arrange themselves in thin films, as shown opposite. We can use these more detailed descriptions of molecular structure to examine the links between molecular arrangement and charge transport as a function of regio-regularity, molecular weight and poly-dispersity – allowing greater precision of charge transport simulations than is possible using traditional KMC methods.

Key papers:

Groves C 2013. Charge Recombination in Organic Photovoltaic Devices with a Cascaded Energy HeterojunctionEnergy & Environmental Science 6(5): 1546-1551. (review)

Jones ML, Huang DM, Charkrabarti B, Groves C 2016. Relating Molecular Morphology to Charge Mobility in Semicrystalline Conjugated Polymers – Journal of Chemical Physics C 120(8):4240-4250.

Noise Spectroscopy

Measuring the fluctuation of electrical current can provide detailed information about the energetic and morphological structure of organic materials. For example, the image below presents the noise spectra of annealed and non-annealed P3HT:PCBM photovoltaic devices. The higher flicker noise level of the annealed device is attributed to increased heterogeneity in the current flowing though the device, related to a more heterogeneous P3HT:PCBM bulk heterojunction (BHJ) morphology.

Key papers:

Kaku K, Williams AT, Mendis BG, Groves C 2015. Examining Charge Transport Networks in Organic Bulk Heterojunction Photovoltaic Diodes using 1/f Noise Spectroscopy – Journal of Materials Chemistry C 3:6077-6085