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Solution-processed bathocuproine (BCP) has been widely used in fullerene (FA)-based organic solar cells (OSCs) for decades as an electron transport layer (ETL).

Despite the outstanding role of conjugated polyelectrolytes (CPEs) in organic solar cells, the use of CPEs in perovskite solar cells has rarely been reported due to instability issues of the material itself under operating conditions.

A simpler and less expensive fabrication process is one of the essential demands for the commercialization of perovskite solar cells (PeSCs). Especially, inverted PeSCs (I-PeSCs) require a cathode buffer layer (CBL) for fabricating highly efficient and stable PeSCs. However, this increases the number of fabrication step. Here, we demonstrate highly stable and efficient cathode-buffer-layer-free I-PeSCs via additive engineering on an ETL, which is based on phenyl-C61-butyric acid methyl ester (PC61BM) with a small amount of poly(methyl methacrylate) (PMMA). This modified ETL shows not only a simplified fabrication process but also effective extraction of charge from the perovskite to a high work function copper electrode (Cu) by formation of an interfacial dipole at the interfaces between the ETL and the Cu. Additionally, it exhibits good passivation of the trap density existing along the grain boundaries and surface of the perovskite layer, reducing the non-radiative recombination and consistent with the increases in open-circuit voltage (Voc). As a result, I-PeSCs with a blend PC61BM : PMMA ETL demonstrate an enhancement in the power conversion efficiency (PCE) from 13.55% (without PMMA) to 18.38%. Furthermore, they exhibit both burn-in-free behaviour in photostability measurements by maximum power-point tracking (MPPT) method and long-term air-stability (30 days for T90) in ambient air. Lastly, we obtained PCE of 15.03% and 16.83% for large-area (1 cm2) I-PeSCs with PC61BM and PC61BM : PMMA, respectively. This method provides an alternative route to reduce the fabrication time and budget for commercialization of I-PeSCs without sacrificing device performance.

Correction for ‘Conjugated polyelectrolytes for stable perovskite solar cells based on methylammonium lead triiodide’ by Yong Ryun Kim et al., J. Mater. Chem. A, 2022, 10, 3321–3329, https://doi.org/10.1039/D1TA10185D.

Despite the promise of simple manufacturing via an entirely solution-based process at low temperature (

Carbazole-based conjugated small molecule electrolytes (CSEs) containing different numbers of amine groups were synthesized and applied to bulk-heterojunction (BHJ) organic solar cells for the formation of a spontaneous self-assembled electron transporting layer (ETL). The active layer was spin-coated with a mixture solution containing the BHJ materials and a small amount of CSE, and a thin layer of CSE was formed underneath the active layer (CSE/BHJ bi-layer) via spontaneous phase separation, which is confirmed by the depth profile of the time of flight secondary ion mass spectroscopy (ToF-SIMS) spectrum. The amino groups in the CSEs form hydrogen-bonds with the surface of indium tin oxide (ITO), which acts as an ETL in BHJ solar cells. Moreover, the formed CSE layer is capable of changing the effective work function (WF) of ITO. An increasing number of amino groups in the CSEs (from Cz1N to Cz3N) provides more reduction of the effective WF of ITO, which results in a lower internal resistance and a higher power conversion efficiency (PCE). Furthermore, the enhanced hydrogen bonding between the amines and ITO with an increased number of amine groups has been studied by XPS. This result suggests that one-step processing provides a reduction of the manufacturing cost, which can provide an attractive design concept for ETL fabrication.