Recent studies have demonstrated that copper (I) thiocyanate (CuSCN) has huge potential as a hole extraction material (HEM) for perovskite solar cells. Here, we used CuSCN as a HEM and analyzed its relationships with a methylammonium lead iodide (MAPbI 3 ) perovskite layer. The CuSCN dissolved in diethyl sulfide (DES) was spin-coated on the MAPbI 3 layer. For high-quality and dense CuSCN layers, post-annealing was carried out at various temperatures and times. However, the unwanted dissociation of MAPbI 3 to PbI 2 was observed due to the postannealing for a long time at elevated temperatures. In addition, DES, which is used as a CuSCN solvent, is a polar solvent that damages the surface of MAPbI 3 perovskites and causes poor interfacial properties between the perovskite layer and HEM. To solve this problem, the effect of the molar ratio of methylammonium iodide (MAI) and PbI 2 in the MAPbI 3 precursor solution was investigated. The excess MAI molar ratio in the MAPbI 3 precursor solution reduced MAPbI 3 surface damage despite using DES polar solvent for CuSCN solution. In addition, dissociation of MAPbI 3 to PbI 2 following an adequate post-annealing process was well suppressed. The excess MAI molar ratio in the MAPbI 3 precursor could be compensated for the MA loss and effectively suppress phase separation from MAPbI 3 to MAI + PbI 2 during post-annealing. The efficiency based on the normal planar structure of CuSCN/MAPbI 3 (using excess MAI)/TiO 2 was approximately 17%. The CuSCN-based MAPbI 3 device shows more optimized stability than the conventional spiro-OMeTAD under damp heat (85 °C and 85% relative humidity) conditions because of the robust inorganic HEM.

Perovskite solar cells (PSCs) have been receiving considerable attention as next-generation solar cells. However, their short lifetime is a major obstacle to their commercialization. In addition to the properties of the materials used in PSCs, their interfaces play an important role in device stability by maintaining their initial design. In this study, we developed a transition-metal dichalcogenide (TMD) as a stable and efficient interlayer. MoS 2 and WSe 2 were applied to both the hole and electron transport sides of the PSCs with general FTO/TiO 2 /MAPbI 3 /Spiro-OMeTAD/Au structures, respectively. Owing to efficient charge transfer by TMD interlayers, our PSCs achieved a 19.24% efficiency, which is higher than the efficiency of the control devices (18.22%). Furthermore, the device stability was markedly improved by the passivation and strain-release effects of the TMD interlayers. Thus, the PSCs with TMD interlayers demonstrated a stable performance over 1000 h under damp heat (85 °C and 85% relative humidity) conditions.

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A novel organic ionic material, hole transport material‐1 (HTM‐I), was synthesized and characterized as a hole transport material for perovskite solar cells (PSCs), with the aim of replacing 2,2',7,7'‐Tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9'‐spirobifluorene (Spiro‐OMeTAD). HTM‐I was designed to incorporate both phenoxazine and benzimidazolium iodide salt structures, and its chemical structure was confirmed using 1H NMR and high‐resolution mass spectrometry. Differential scanning calorimetry measurements revealed that HTM‐I maintained an amorphous phase throughout the temperature range of −60 – 200 °C, and thermogravimetric analysis showed good thermal stability up to 220 °C. To evaluate its potential as a hole transport layer, perovskite solar cells were fabricated using a fluorine‐doped tin oxide (FTO)/compact‐TiO2/(Cs/FA/MA)Pb(I/Br)3/hole transport layer/Au configuration. The resulting n–i–p planar structure exhibited a power conversion efficiency of 10.4%.

TiO 2 thin film typically used as an electron transport layer (ETL) in perovskite solar cells has many advantages such as high refractive index, good photocatalytic properties, excellent chemical stability, and low cost. TiO 2 thin films are typically formed by a solution process, but it is difficult to achieve large area coating, accurate thickness control, and mass production with this process. Here, we demonstrated that radiofrequency (RF)-sputtered TiO 2 is an effective replacement for use as the ETL for the perovskite solar cells in order to overcome the disadvantages of the solution process. The TiO 2 layer was deposited on the substrate by reactive sputtering (RS) with a high-purity Ti metal target. The RFRS TiO 2 thin film was systematically characterized and compared with spin-coated TiO 2 by means of various analytical techniques. The transmittance of 20-nm-thick as-deposited TiO 2 on an indium tin oxide (ITO)-coated glass substrate was 75−80 % in the visible range. After annealing, the amorphous phase was converted into an anatase structure in RFRS TiO 2 . In the case of the spin-coated TiO 2 layer, indium diffusion from the ITO layer and an increase in sheet resistance with the annealing temperature were observed. On the other hand, the RFRS TiO 2 had a denser and more uniform surface, and it could be annealed at a lower temperature. Therefore, it was able to block indium diffusion and increase the 𝑉 OC and FF values. Finally, the device efficiency of the perovskite solar cell was improved from 16.04 to 17.46 % when using RFRS TiO 2 as the ETL.