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For efficient perovskite solar cells (PSCs), hole transport layers (HTLs) are necessary components that can suppress recombination by collecting holes and blocking electrons. Inorganic hole transport materials (HTMs) are attractive because of their ease of preparation, low production cost and high stability. Although metal oxides and halides have been developed as the HTMs, metal hydroxides have not yet been reported as the HTMs of PSCs. In this work, copper doped lanthanum hydroxide (La x Cu y (OH) 3) nanorods were firstly synthesized by the hydrothermal method as a new kind of HTM for PSCs. Although the valence band edge of La(OH) 3 is slightly mismatch with that of perovskite layers, Cu2+ dopants improve the energy level alignment at HTL/perovskite interfaces. As an acceptor dopant for La(OH) 3 , Cu2+ ions also increase the hole transport ability of La x Cu y (OH) 3 HTLs. Additionally, La x Cu y (OH) 3 HTLs tend to encourage the crystallization of perovskite layers. As a consequence, Cu2+ dopants lead to an increase of PCE from 11.3 % to 20.4 % for La x Cu y (OH) 3 based PSCs. This promotion can be related to the reduced recombination process and the elevated charge extraction process. This work firstly applied metal hydroxide as the HTMs of PSCs, and demonstrates the regulation of these HTMs by the doping method. [Display omitted] • La(OH) 3 nanorods with copper dopants (La x Cu y (OH) 3) were synthesized. • La x Cu y (OH) 3 films were deposited by spin-coating at a low temperature of 100 °C. • Energy level and hole transport ability were improved by incorporating Cu2+ ions. • The Cu2+ dopants can also promote the crystallization of perovskite layers. • Cu2+ dopants lead to an improvement of PCEs from 11.3 % to 20.4 % for PSCs. [ABSTRACT FROM AUTHOR]

Electron transport layers can collect photo-generated electrons and suppress interfacial recombination, which are crucial for efficient perovskite solar cells. Tin oxide is a suitable electron transport material for its wide bandgap, high electron mobility, low photocatalytic activity and appropriate energy band offsets. For the deposition of tin oxide layers, SnCl 2 precursor is usually used for the conventional solution spin-coating method. In this work, we developed an in-situ synthesized precursor, and ultrathin tin oxide layers were obtained by the combustion process at 150 °C. Furthermore, the devices with these tin oxide layers can achieve the PCE of 19.6%, while conventional tin oxide layers with SnCl 2 precursor lead to the PCEs of 16.9% and 14.9% with and without plasma treatment. This improvement can be related to the enhanced photoelectron collection and superior interfacial contact. This work provides a facile method for fabricating SnO 2 electron transport layers of perovskite solar cells at low temperature. [Display omitted] • A novel SnO 2 precursor solution was developed by the in-situ synthesis from tin powder. • SnO 2 ETLs with high purity were prepared by the combustion process at low temperature. • Ultrathin SnO 2 ETLs were obtained with enhanced charge collection and interfacial contact. • PSCs with newly developed SnO 2 ETLs were superior to devices by conventional SnCl 2 precursor. [ABSTRACT FROM AUTHOR]