Abstract
The commercialization of perovskite solar cells (PSCs) has seen an important limitation in the instability that afflicts the hole-transporting layer (HTL), namely, spiro-OMeTAD, used in high-efficiency devices. The latter is, in turn, relatively expensive, undermining the sustainability of the device. Its replacement with polymeric scaffolds, such as poly(3-hexylthiophene) (P3HT), will solve these issues. In this work, we adopted various sustainable synthetic methods to obtain four different homemade P3HTs with different molecular weights (MWs) and regioregularities (RRs), leading to different structural properties. They are implemented as HTLs in PSCs, and the effect of their properties on the efficiency and thermal stability of devices is thoroughly discussed. The highest efficiency is obtained with the highest MW and low-RR polymer (17.6%) owing to the more sustainable approach, but a very promising value is also reached with a lower-MW but fully regioregular polymer (15%). Finally, large-area devices with an efficiency of 16.7%, fabricated with a high-MW P3HT, show more than 1000 h (T80 = 1108 h) of stability under accelerated thermal stress tests (85 °C) out of glovebox while keeping over 85% of the initial efficiency of an unencapsulated device after more than 3000 min under continuous light soaking (AM 1.5G).
Highlights
The attention drawn by photovoltaic (PV) technologies based on hybrid organic−inorganic perovskite (PSK)-structured materials in these years is justified by the tremendous improvement in the power-conversion efficiency (PCE) that they have witnessed in less than a decade, going from just 3.8% up to 25.5%.1−3 Such amazing PCE values in addition to the relatively low energy payback time (EPBT) and cost-effective solution-based production make perovskite solar cells (PSCs) a promising sustainable alternative for the near-future PV market.[4−6] one of the main limitations preventing perovskites from entering the PV market is the concern regarding their stability.[7−10] To comply with IEC standard 61215, thin-film PV devices should pass, among others, a damp heat stability test at 85 °C with 85% relative humidity (RH) for
We investigate the thermal behavior of four homemade P3HTs with different combinations of molecular weight (MW)/RRs, namely, 19 kDa/95%, 194 kDa/100%, 223 kDa/79%, and 338 kDa/76%, and their influence on the thermal stability of mixed-cation ((FAPbI3)0.81(MAPbBr3)0.14(CsI)0.05) perovskite solar cells
A lowMW (19 kDa/95%) P3HT was prepared by the direct arylation protocol (DArP) method (Scheme 1, path a), showing a 95% RR,[62] while the GRIM (Grignard methathesis) method gave a very-high-MW P3HT (194 kDa/100%) with full RR (Scheme 1, path b).[62,63]
Summary
The reported results would hint at the fact that shorter polymer chains hinder charge extraction from the perovskite active layer, reducing the FF; this results in a higher nonradiative recombination rate at the interface, which jeopardizes the Voc of the device.[69,70] On the other hand, the improvement in Jsc could be related to the better hole mobility of high-MW P3HT compared to the low-MW one.
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