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Inorganic electron transport layers (ETLs), such as titanium dioxide (TiO 2 ) and tin dioxide (SnO 2 ), are important in n−i−p structured perovskite solar cells (PSCs). In particular, the ETLs for flexible PSCs (f-PSCs) using a polymer substrate require strong adhesion with a transparent conducting oxide (TCO) and formation of a uniform thin film at a temperature below 150 °C. Hence, SnO 2 colloidal nanoparticles are primarily used to meet these demands. Nevertheless, there exist further opportunities for improvement in terms of efficiency, uniform coating, and adhesion on TCO. In this study, we prepared a SnO 2 −TiO 2 hybrid electrode by adding a certain amount of TiO 2 nanosol, which functions as an inorganic binder, to a SnO 2 colloidal solution. In comparison with the SnO 2 colloid alone, f-PSC fabricated with a SnO 2 −TiO 2 hybrid electrode demonstrated not only better mechanical reliability against bending due to strong adhesion to the substrate but also greatly improved efficiency because of improved energy alignment. Eventually, the SnO 2 −TiO 2 hybrid electrode resulted in an efficiency of 21.02% and even an efficiency of over 16% in a mini-module (7 × 7 cm 2 ) due to the uniform coating over a large area. This study provides a new strategy for the ETL of high-efficiency f-PSCs.

To expedite the commercialization of perovskite solar cells (PSCs), researchers are exploring the feasibility of employing nickel phthalocyanine (NiPc) as a hole transport material (HTM) due to its cost‐effectiveness, excellent thermal stability, and suitability for solution coating. However, the low LUMO energy level of the NiPc may limit its ability to block photoelectrons generated in the perovskite layer from recombining with holes, which can reduce the overall efficiency of the solar cell. One solution is to use cascaded bilayers with HTMs that have relatively higher LUMO levels. In this study, a bilayer consisting of NiPc and poly(3‐hexylthiophene) (P3HT) is employed as the HTM, where the P3HT exhibits vertical phase separation during the coating process. By optimizing the mixing amount of P3HT into the NiPc, a record power conversion efficiency of 23.11%, the highest reported for NiPc‐based PSCs is achieved. Moreover, an excellent long‐term stability is demonstrated by encapsulating the PSC in polyisobutylene, with the device retaining 90% of its initial efficiency after exposure to 85 °C and 85% relative humidity for 1000 h.

Improving the performance, reproducibility, and stability of Sn-based perovskite solar cells (PSCs) with n-i-p structures is an important challenge. Spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], a hole transporting material (HTM) with n-i-p structure, requires the oxygen exposure after addition of Li-TFSI [Lithium bis(trifluoromethanesulfonyl) imide] as a dopant to increase the hole concentration. In Sn-based PSC, Sn 2+ is easily oxidized to Sn 4+ under such a condition, resulting in a sharp decrease in efficiency. Herein, a formamidinium tin triiodide (FASnI 3 )-based PSCs fabricated using DPI-TPFB [4-Isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate] instead of Li-TFSI are reported as a dopant in Spiro-OMeTAD. The DPI-TPFB enables the fabrication of PSCs with an efficiency of up to 10.9%, the highest among FASnI 3 -based PSCs with n-i-p structures. Moreover, ≈80% of the initial efficiency is maintained even after 1,597 h under maximum power point tracking conditions. In particular, the encapsulated device does not show any decrease in efficiency even after holding for 50 h in the 85 °C/85% RH condition. The high efficiency and excellent stability of PSCs prepared by doping with DPI-TPFB are attributed to not only increasing electrical conductivity by acting as a Lewis acid, but also stabilizing Sn 2+ through coordination with Sn 2+ on the surface of FASnI 3 .