Recombination layers cells

A typical organic tandem cell consists of two subcells stacked on top of each other, each of which has different absorption range (Figure 12.8). The two subcells are connected in series via a thin recombination layer. Hence, better coverage of the solar spectrum and reduction of the thermalization loss can be realized due to the use of materials with different bandgaps. The total thickness of the active films in... 

Drachuk I, et al. Silk macromolecules with amino acid poly(ethylene glycol) grafts for controlling layer-by-layer encapsulation and aggregation of recombinant bacterial cells. ACS Nano 2015 9(2) 1219-35. 

Figure 11.2 Schematic representations of the regular and inverted device layouts for series-connected organic tandem cells. Under operation the indium tin oxide (ITO) electrode is biased positive with respect to the metal electrode in the regular configuration and negative in the inverted configuration. The difference is caused hy the positioning of the hole and electron collecting layers (HCL and ECL) with respect to photoactive layers. The intermediate contact formed hy HCL and ECL is referred to as the recombination layer. Note that in practice the device layout may vary from these schematics.

The next step was the use of solution processed charge transport layers in the recombination contact of polymer solar cells. In 2007, Gilot et al showed that ZnO nanoparticles processed from acetone can be covered with a layer of pH-neutral PEDOTrPSS spincoated from a dispersion in water to fabricate a ZnO/PEDOT PSS recombination layer that is transparent to light and makes an almost loss-less recombination layer for tandem and triple junction cells. This approach bears similarity to the p- and n-doped wide bandgap transport layers developed for evaporated small molecule tandem cells. The ZnO/PEDOT PSS recombination contact was initially employed in... 

Several excellent reviews exist on polymer tandem solar cells and we refer to these publications for a comprehensive overview. In this chapter we focus on the materials requirements for creating efficient polymer solar cells and intermediate contact layers. In the following paragraphs, we will outline the operational principles in more detail. We will then review the most important photoactive materials used in polymer multi-junction cells and outline the material combinations that can used for the recombination layer. We conclude with an overview of recent achievements that have pushed the efficiency to well over 10% and address the progress in processing of large area tandem polymer solar cells. 

Next to efficient active layer materials, the other critical component of a tandem solar cell is the intermediate contact layer or recombination layer. This layer is responsible for the electrical connection of the subcells and the effective operation of the device. There is no current generation in this area and... 

Figure 11.12 Device structure of the polymer tandem solar cells with PEDOT PSS (PHIOOO) modified by PEIE as the recombination layer. Reproduced from ref. 67.

Polymer multi-junction cells have also achieved noticeable attention. In Table 11.2 we provide an overview of the multi-junction cells that had been published up to the end of 2014. In 2007, Gilot et al showed that it is possible fully to solution process three photoactive layers and two recombination layers based on ZnO/PEDO PSS and obtain a working triple junction solar cell with koc = 2. 19 By the same procedure, six-fold junction cells with... 

Cell configuration" (eV) Foe (V) lype PCE (%) Recombination layer front/back Ref. 

In 2010, Yang et al published the first inverted configuration tandem polymer solar cell using P3HT PC6iBM and PSBTBT PC7iBM subcells. As a recombination layer, Yang et al used thermally evaporated MoOj and Al, covered with a sol-gel ZnO layer to reach a PCE of 5.1%. Almost at the same... 

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