The study of the inorganic hole-transport layer (HTL) in perovskite solar cells (PSCs) is gathering attention because of the drawback of the conventional PSC design, where the organic HTL with salt dopants majorly participates in the degradation mechanisms. On the other hand, inorganic HTL secures better stability, while it offers difficulties in the deposition and interfacial control to realize high-performing devices. In this study, we demonstrate polydimethylsiloxane (PDMS) as an ideal polymeric interlayer which prevents interfacial degradation and improves both photovoltaic performance and stability of CuSCN-based PSC by its cross-linking behavior. Surprisingly, the PDMS polymers are identified to form chemical bonds with perovskite and CuSCN, as shown by Raman spectroscopy. This novel cross-linking interlayer of PDMS enhances the hole-transporting property at the interface and passivates the interfacial defects, realizing the PSC with high power-conversion efficiency over 19%. Furthermore, the utilization of the PDMS interlayer greatly improves the stability of solar cells against both humidity and heat by mitigating the interfacial defects and interdiffusion. The PDMS-interlayered PSCs retained over 90% of the initial efficiencies, both after 1000 h under ambient conditions (unencapsulated) and after 500 h under 85 °C/85% relative humidity (encapsulated).

Interfacial degradation in perovskite solar cells is a critical issue affecting long-term stability for future commercialization. In particular, a perovskite and an organic hole-transport layer (HTL) react easily when the device is exposed to extreme operating conditions (heat, light, and air). To prevent degradation, an inorganic CuSCN HTL has emerged as an alternative, yet the interfacial reactivity is still not clearly elucidated. Herein, Cu 2 O and CuSCN are coutilized to form an efficient and stable HTL. While uniform film formation using Cu 2 O is difficult despite its high mobility, a Cu 2 O− CuSCN nanocomposite can be excellently synthesized as an effective HTL, exhibiting a power conversion efficiency (PCE) of 19.2% and sustaining its PCE over 90% for 720 h under extreme conditions (85 °C/85% of relative humidity, encapsulated). A chemical distribution analysis by secondary-ion mass spectroscopy (SIMS) suggests that a Cu 2 O nanoparticle layer protects the interface between the perovskite and CuSCN. The optoelectronic properties of the nanocomposite HTL and the improved solar cell performance are correlated with the recombination rate, electronic trap distribution in the band gap, and charge extraction efficiencies.

Operational stability of perovskite solar cells has been a challenge from the beginning of perovskite research. In general, humidity and heat are the most well‐known degradation sources for perovskites, requiring ideal design of perovskite chemistry to withstand them. Although triple‐cation perovskite (Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3) has been already introduced as the stable perovskite material, the high reactivity of methylammonium and formamidinium in the cation sites demands further modification. Herein, 1,2,4‐triazole is suggested as an effective cation solute to improve the performance and stability of perovskite solar cells. 1,2,4‐Triazole is an aromatic cation with low dipole moment that is stable under humidity and heat. It also possesses three nitrogen atoms, forming additional hydrogen bonds in the lattice, stabilizing the material. In this study, the solar cell utilizing 1,2,4‐triazole alloying achieves a power conversion efficiency of 20.9% with superior stability under extreme condition (85 °C/85% of relative humidity (RH), encapsulated) for 700 h. The 1,2,4‐triazole‐alloyed perovskite exhibits reduced trap density and film roughness and enhanced carrier lifetime with electrical conductivity, suggesting an ideal perovskite structure for efficient and stable optoelectronic applications.