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).

Recently, SnO2 has been noticed as a promising material for electron-transport layer of planar perovskite solar cells. SnO2 layer presents advantages of low-temperature processability and high power-conversion efficiency, and understanding the correlations between the SnO2 properties and device performance will provide a key to realize more efficient perovskite solar cells. Herein, uniform electron-transport layer using SnO2 nanoparticles is fabricated, and the effect of annealing on the solar-cell performance is discussed. Solar cells with low-temperature processed SnO2-nanoparticle layer (below 120 °C or even at room temperature) exhibit desirable short-circuit current, open-circuit voltage, and fill factor with the highest efficiency of 19.0%. Using atomic force microscopy and ultraviolet photoelectron spectroscopy, both great surface uniformity and favorable band alignment of low-temperature processed SnO2 layer have been observed, which are responsible for the device performance. Furthermore, deep electronic-trap states at the SnO2/perovskite interface are investigated via impedance analysis. Compared to the cells processed over 160 °C, low-temperature processed cells exhibit trap states shifting toward the bandedge and reduced trap density, verifying that controlling the interfacial trap states holds a dominance on the open-circuit voltage and is a critical requisite to enable efficient perovskite solar cells. These less-defective solar cells fabricated below 120 °C show high thermal stability, suggesting further commercial applications.

Herein, underlying factors for enabling efficient and stable performance of perovskite solar cells are studied through nanostructural controls of organic−inorganic halide perovskites. Namely, MAPbI 3 , (FA 0.83 MA 0.17 )Pb(I 0.83 Br 0.17 ) 3 , and (Cs 0.10 FA 0.75 MA 0.15 )Pb(I 0.85 Br 0.15 ) 3 perovskites (abbreviated as MA, FAMA, and CsFAMA, respectively) are examined with a grain growth control through thermal annealing. FAMA-and CsFAMA-based cells result in stable photovoltaic performance, while MA cells are sensitively dependent on the perovskite grain size dominated by annealing time. Micro-/nanoscopic features are comprehensively analyzed to unravel the origin that is directly correlated to the cell performance with the applications of electronic-trap characterizations such as photoconductive noise microscopy and capacitance analyses. It is revealed that CsFAMA has a lower trap density compared to MA and FAMA through the analyses of 1/f noises and trapping/detrapping capacitances. Also, an open-circuit voltage (V oc ) change is correlated to the variation of trap states during the shelf-life test: FAMA and CsFAMA cells with the negligible change of V oc over weeks exhibit trap states shifting toward the band edge, although the power-conversion efficiencies are clearly reduced. The origins that critically affect the solar cell performance through the characterizations of shallow/deep traps with additional mobile defects in the perovskite and interfaces are discussed.

Moving away from the high-performance achievements in organometal halide perovskite (OHP)-based optoelectronic and photovoltaic devices, intriguing features have been reported in that photocarriers and mobile ionic species within OHPs interact with light, electric fields, or a combination of both, which induces both spatial and temporal changes of optoelectronic properties in OHPs. Since it is revealed that the transport of photocarriers and the migration of ionic species are affected not only by each other but also by the inhomogeneous character, which is a consequence of the route selected to deposit OHPs, understanding the nanostructural evolution during OHP deposition, in terms of the resultant structural defects, electronic traps, and nanoscopic charge behaviors, will be valuable. Investigation of the film-growth mechanisms and strategies adopted to realize OHP films with less-defective large grains is of central importance, considering that single-crystalline OHPs have exhibited the most beneficial properties, including carrier lifetimes. Critical factors governing the behavior of photocarriers, mobile ionic species, and nanoscale optoelectronic properties resulting from either or all of them are further summarized, which may potentially limit or broaden the optoelectronic and photovoltaic applications of OHPs. Through inspection of the recent advances, a comprehensive picture and future perspective of OHPs are provided.

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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.

Because of the facile formation of defects in organometal halide perovskites, the defect passivation has become an important prerequisite for the stable and efficient perovskite solar cell (PSC). Regarding that ionic defects of the perovskites play a significant role on the performance and stability of PSCs, we introduce lithium fluorides as effective passivators based on their strong ionic characteristics and small ionic radii. Both Li+ and F– are observed to successfully incorporate within the perovskite layer, improving the device performances with the best efficiency over 20%, while the hysteresis effects are significantly reduced, confirming the passivation of perovskite defects. Moreover, LiF restrains both thermal degradation and photodegradation of PSCs, where over 90% of the initial efficiencies have been retained by LiF-incorporated devices for more than 1000 h under either 1 sun illumination or 85 °C thermal condition. As the trap density of states is analyzed before and after the thermal stress, not only the mitigation of electronic traps as fabricated but also the dramatic relaxation of traps during the postannealing step is observed with the LiF incorporation. From this work, LiF has shown its potential as a promising ionic passivator, and the phenomenal achievement of device stability by LiF provides a clear insight to overcome the stability issues of PSCs, a key to the commercialization of next-generation photovoltaics.

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.