Keith Gregory Brooks

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Foldable Hole-Transporting Materials for Merging Electronic States between Defective and Perfect Perovskite Sites

Keith Gregory Brooks, Paul Joseph Dyson, Ruiyuan Hu, Hiroyuki Kanda, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Jianxing Xia, Yi Zhang

Defective and perfect sites naturally exist within electronic semiconductors, and considerable efforts to reduce defects to improve the performance of electronic devices, especially in hybrid organic-inorganic perovskites (ABX(3)), are undertaken. Herein, foldable hole-transporting materials (HTMs) are developed, and they extend the wavefunctions of A-site cations of perovskite, which, as hybridized electronic states, link the trap states (defective site) and valence band edge (perfect site) between the naturally defective and perfect sites of the perovskite surface, finally converting the discrete trap states of the perovskite as the continuous valence band to reduce trap recombination. Tailoring the foldability of the HTMs tunes the wavefunctions between defective and perfect surface sites, allowing the power conversion efficiency of a small cell to reach 23.22% and that of a mini-module (6.5 x 7 cm, active area = 30.24 cm(2)) to reach as high as 21.71% with a fill factor of 81%, the highest value reported for non-spiro-OMeTAD-based perovskite solar modules.

WILEY-V C H VERLAG GMBH2023

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Despite recent increases in perovskite solar cell (PSC) efficiencies, long-term stability remains a barrier to manufacturing and marketing. SnO2 electron transport layers enable the low-temperature processing of planer n-i-p structured PSCs. However, ultraviolet radiation damages to the interface between the electron transport layer and the perovskite (PVK), which is a significant issue for n-i-p configuration. Herein, the insertion of a thin CeO2 passivation layer between the SnO2 and PVK is investigated to block the interface degradation. This CeO2 layer improves charge extraction and reduces defects in the PVK/CeO2 interface, resulting in 22.71% power conversion efficiency (PCE) compared to the pristine SnO2 PSC devices, which has a PCE of 20.7%. In addition, after 1700 h of storage at room temperature and 5%-8% RH (dry box), the PCE stability of the reinforced SnO2-CeO2 PSC devices drops from 22% to 19%, whereas that of the pristine SnO2 PSC devices drops from 20% to 16%.

WILEY2023

Bifunctional additive 2-amino-3-hydroxypyridine for stable and high-efficiency tin-lead perovskite solar cells

Keith Gregory Brooks, Mohammad Khaja Nazeeruddin, Yi Zhang, Bing Zhang

Tin-lead (Sn-Pb) mixed perovskite has received widespread attention due to its suitable band gap width and high optical absorption coefficients. However, the power conversion efficiency (PCE) of Sn-Pb mixed perovskite solar cells (PSCs) is still low due to the fact that Sn2+ could be easily oxidized to Sn4+ and an excessively rapid crystallization rate was observed for the Sn-Pb mixed perovskite materials. Herein, we introduced 2-amino-3-hydroxypyridine (AHPD), which contains a pyridine nitrogen and an -NH2 group in the molecule, as a bidentate anchoring additive in the FA(0.7)MA(0.3)Pb(0.5)Sn(0.5)I(3) precursor solution to improve device performance. Incorporation of AHPD into the FA(0.7)MA(0.3)Pb(0.5)Sn(0.5)I(3) precursor solution was found to effectively suppress the Sn2+ oxidation and thus the p-doping level defects. Furthermore, the pyridine nitrogen and the enamine-like -NH2 could retard the nucleation and crystallization rate by forming a coordinating interaction with PbI2/SnI2, forming compact large-grained films and also improving the carrier transport by passivation of the grain boundaries. Overall, compared with the control device (a PCE of 15.72%), an optimized device incorporating 2 mol% AHPD exhibited a PCE of 19.18% for narrow band gap perovskite solar cells, an increase of nearly 22%, with a high level of reproducibility.

ROYAL SOC CHEMISTRY2022