Employing Equivalent Circuit Models to Study the Performance of Selenium-Based Solar Cells with Polymers as Hole Transport Layers

Sustainable Recycling of Selenium-Based Optoelectronic Devices

Selenium (Se), the world's oldest optoelectronic material, has been widely applied in various optoelectronic devices such as commercial X-ray flat-panel detectors and photovoltaics. However, despite the rare and widely-dispersed nature of Se element, a sustainable recycling of Se and other valuable materials from spent Se-based devices has not been developed so far. Here a sustainable strategy is reported that makes use of the significantly higher vapor pressure of volatile Se compared to other functional layers to recycle all of them from end-of-life Se-based devices through a closed-space evaporation process, utilizing Se photovoltaic devices as a case study. This strategy results in high recycling yields of ≈ 98% for Se and 100% for other functional materials including valuable gold electrodes and glass/FTO/TiO2 substrates. The refabricated photovoltaic devices based on these recycled materials achieve an efficiency of 12.33% under 1000-lux indoor illumination, comparable to devices fabricated using commercially sourced materials and surpassing the current indoor photovoltaic industry standard of amorphous silicon cells.

Blending Donors with Different Molecular Weights: An Efficient Strategy to Resolve the Conflict between Coherence Length and Intermixed Phase in Polymer/Nonfullerene Solar Cells

Long coherence lengths (CLs) of crystals and proper intermixed phase amount guarantee charge transport and exciton dissociate efficiently, which is crucial for organic solar cells (OSCs) to achieve high device performance. However, extending CLs usually reduces the intermixed phase, leading to an insufficient interface for exciton dissociation. Herein, a strategy using a binary polymer with different molecular weights as donor is employed, that is, poly(3-hexylthiophene-2,5-diyl) (P3HT) with high (P3HT-H) and low (P3HT-L) molecular weight are blended as donor, and (5Z,5'Z)-5,5'-(((4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) (O-IDTBR) is used as acceptor. In kinetics, the entanglements of P3HT-H are relieved due to the higher molecular diffusivity of P3HT-L. In thermodynamics, the miscibility of P3HT-L/O-IDTBR, P3HT-H/O-IDTBR, and P3HT-L/P3HT-H blends increases in turn. Hence, P3HT forms a more ordered structure with longer CLs after adding P3HT-L, which also drives O-IDTBR dispersed in P3HT crystalline regions diffuse to the O-IDTBR crystalline regions to further self-organize. Consequently, the CLs of both P3HT and O-IDTBR are extended, while keeping the intermixed phase amount proper. The optimized microstructure boosts device performance from 7.03% to 7.80%, which is one of the highest values reported for P3HT/O-IDTBR blends. This is a novel way to solve the conflict mentioned above, which may provide guidance to finely regulating the morphology of the active layer.