Fabrication Processes to Generate Concentration Gradients in Polymer Solar Cell Active Layers

Abstract

Polymer solar cells (PSCs) are considered as one of the most promising low-cost alternatives for renewable energy production with devices now reaching power conversion efficiencies (PCEs) above the milestone value of 10%. These enhanced performances were achieved by developing new electron-donor (ED) and electron-acceptor (EA) materials as well as finding the adequate morphologies in either bulk heterojunction or sequentially deposited active layers. In particular, producing adequate vertical concentration gradients with higher concentrations of ED and EA close to the anode and cathode, respectively, results in an improved charge collection and consequently higher photovoltaic parameters such as the fill factor. In this review, we relate processes to generate active layers with ED–EA vertical concentration gradients. After summarizing the formation of such concentration gradients in single layer active layers through processes such as annealing or additives, we will verify that sequential deposition of multilayered active layers can be an efficient approach to remarkably increase the fill factor and PCE of PSCs. In fact, applying this challenging approach to fabricate inverted architecture PSCs has the potential to generate low-cost, high efficiency and stable devices, which may revolutionize worldwide energy demand and/or help develop next generation devices such as semi-transparent photovoltaic windows.

Electrochemical and Spectroelectrochemical Studies on the Reactivity of Perimidine–Carbazole–Thiophene Monomers towards the Formation of Multidimensional Macromolecules versus Stable π-Dimeric States

“…It is noteworthy that supramolecular polymers do not comply with classical Carothers' definition of a polymer as a single macromolecule but rather the idea of polymers as colloidal aggregates. Morphology of π-conjugated one-dimensional polymer is also determined by self-assembly processes and so molecular packing and orientation during crystallization initiated by: π-π interactions between aromatic rings e.g., in poly(3hexylthiophene) (P3HT) [19], oligo(pyrrole)s [20,21], directional and strong H-bonding interactions [22] and coordination bonds [23]. Different types of covalent bonding with accompanying long-range molecular interactions are present in low-band polymers such as multidimensional donor-acceptor systems [24,25] and conjugated ladder polymers (cLP) [26][27][28], where covalent bonds are formed through polymerization while noncovalent bonds can be generated simultaneously because of the dynamic and spontaneous nature of the noncovalent bonds [29].…”

Sequentially Deposited versus Conventional Nonfullerene Organic Solar Cells: Interfacial Trap States, Vertical Stratification, and Exciton Dissociation

“…[36][37][38][39] A method to prepare GBHJ originating from fullerene-based cells, called sequential deposition (sq-BHJ), or layer-by-layer approach attracted much attention last year in developing highefficiency NFA-based OSCs. [40][41][42][43][44][45][46][47] To better control the phase separation, Hou et al used a mixed solvent for a new polymer in combination with a high-performance NFA where the interdiffusion was controlled by the amount of a second solvent. This exercise led to an efficiency at 13% for sq-BHJ devices, higher than 11.8% obtained by the one-step processing.…”

Eco-Friendly Push-Coated Polymer Solar Cells with No Active Material Wastes Yield Power Conversion Efficiencies over 5.5%

“…At 70 °C, DCB desorbs from PDMS faster than at room temperature and consequently, the PC devices prepared at 70 °C for 5 min exhibit very similar performances to unannealed SC devices because of fast drying. Solvent annealing, on the other hand, produces crystalline transformation in thin active layers much faster than thermal annealing. , This is clearly evidenced by the nanoaggregate-like surface of 5 and 10 min PC films which cannot be found in annealed SC active layers or those push-coated for 1 min (Figure ). Unlike previous studies on pure PCDTBT thin films, because of the low PCDTBT content in the blend active layers, we could not observe a crystalline transformation/ordering of the polymer in the X-ray diffraction spectra of the active layers presented in this study.…”