• Energy Research

Abstract

The first report of sub-4 nm mapping of donor : acceptor nanoparticle composition in eco-friendly colloidal dispersions for organic electronics.

‘Soft’ nanoparticles for low temperature processes and highly efficient water-processed organic solar cells.

Abstract Solution processing is mandatory to continue the development of large scale and low cost organic solar cells. Tungsten oxide (WO3) has shown good performance when used as a hole transporting layer in organic solar cells. Here this oxide has been deposited by a sol–gel technique on top of the active layer in an inverted structure device. This layer has been characterised by XPS and UPS to understand the effect of the stoichiometry and of the energy levels on the device performance. In the optimised structure, an average power conversion efficiency (PCE) of 3.5% has been achieved, which is comparable to devices with vacuum deposited transition metal oxide using poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) as an active layer. Moreover in our study no annealing is needed after the deposition of the sol–gel processed oxide, which is really promising for the development of industrial roll-to-roll production on flexible substrates.

Borondifluoride complexes of curcuminoid derivatives end-capped with triphenylamine groups were designed for solution-processed bulk-heterojunction organic solar cells. They were obtained very simply in a one-pot synthesis from cheap building blocks. Compared to push–pull systems based on borondifluoride complexes of hydroxychalcones, curcuminoids present the donor–acceptor–donor electronic structure and exhibit significantly improved chemical and thermal stability and photovoltaic performance. Indeed, power conversion efficiency up to 4.14% and high open-circuit voltage over 1.0 V have been achieved using PC61BM as acceptor.

The search for ever higher efficiency solar cells is at present focussed on multijunction devices. In this field, there is enormous research on tandems consisting of a high bandgap top sub-cell coupled to a Si bottom sub-cell . An emerging top cell candidate is the organic solar cell, given recent impressive breakthroughs in efficiency and stability , thanks in part to non-fullerene ac-ceptors. In this context, we report on approaches to modelling organic solar cells for silicon / organic tandems. The device studied is the three-terminal selective band-offset tandem cell . This innovative design shown in figure 1a is based on the Si interdigitated back contact solar cell , which features a number of fabrication and operating advantages over four terminal and two terminal tandems . The higher gap organic top sub-cell consists of donor and acceptor organic phases in an absorber blend, contacted to hole and electron transport layers, which is in devel-opment within the French ANR project ORGANIST. The modelling of the organic sub-cell is the main focus of this presentation, and is investigated with increasing levels model complexity. The modelling of the complete tandem is first described with a simple first approximation which only considers idealised classic drift-diffusion phenomena of inorganic semiconductors, with optical and band structure data from current best estimates of suitable non-fullerene high bandgap organic solar cell materials . It is shown that this approach is sufficient to quantitatively predict tandem efficiencies with suitable approximations for optical and transport parameters. Figure 1b shows the resulting quantum efficiency of a preliminary 26% tandem without device optimisation, and with a non-textured Si IBC. Organic modelling is then developed from stand-ard open access models , by moving from the widespread effective medium approach treating the absorber blend as a homogeneous material, to a bulk heterojunction model where the accep-tor and donor organic phases are simulated separately. We conclude with lessons learned on the comparative benefits of the modelling approaches for the design and development of high effi-ciency organic solar cells.

The fabrication and the optimization of photovoltaic solar cells based on poly(3,3-didodecylquaterthiophene) (12-PQT) blended with [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) are reported. On the one hand, the effect of the blend composition shows the necessity to increase the amount of fullerene derivative compared to conventional poly(3-hexylthiophene)-based systems. On the second hand, thermal annealing of devices is optimized and discussed. Overall, in this work, the highest power conversion efficiencies are shown in the range of 0.3–0.4% which represents a lower value than that reported with poly(3-hexylthiophene). Results are discussed in terms of charge carrier mobility and phase segregation in this bicontinuous donor-acceptor network.