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Perovskite solar cells (PSCs) have demonstrated rapid progress in their power conversion efficiencies (PCEs)—from 3.8% in 2009 to 25.7% in 2022—and they have received considerable attention as a promising future photovoltaic (PV) technology. However, the operational stability of PSCs is still inadequate to satisfy the standards for commercial applications. Interface engineering has become one of the most important strategies to push PSCs' efficiency and stability for practical use. Among the various interface engineering approaches, organic interface modifiers (OIMs) have been frequently used by the PSC field to address the issues limiting PSC stability at high efficiency levels. In this perspective, the chemical structures of state‐of‐the‐art OIMs are discussed, and their characteristics are reviewed, as well as the impact on device performance associated with key device interfaces (e.g., metal oxide/perovskite and organic transport layer/perovskite interfaces) from a chemical and materials engineering point of view is discussed. Design considerations and the authors' perspective are discussed, on the basis of representative literature examples, for building new, customized organic OIMs to further improve PSC efficiency and stability toward commercialization. [ABSTRACT FROM AUTHOR]

Charge carriers' density, their lifetime, mobility, and the existence of trap states are strongly affected by the microscopic morphologies of perovskite films, and have a direct influence on the photovoltaic performance. Here, we report on micro-wrinkled perovskite layers to enhance photocarrier transport performances. By utilizing temperature-dependent miscibility of dimethyl sulfoxide with diethyl ether, the geometry of the microscopic wrinkles of the perovskite films are controlled. Wrinkling is pronounced as temperature of diethyl ether (TDE) decreases due to the compressive stress relaxation of the thin rigid film-capped viscoelastic layer. Time-correlated single-photon counting reveals longer carrier lifetime at the hill sites than at the valley sites. The wrinkled morphology formed at TDE = 5 °C shows higher power conversion efficiency (PCE) and better stability than the flat one formed at TDE = 30 °C. Interfacial and additive engineering improve further PCE to 23.02%. This study provides important insight into correlation between lattice strain and carrier properties in perovskite photovoltaics. Perovskite morphology dictates carriers' behaviors and defect states, and thus the ultimate performance of the material. Here, the authors investigate micro-wrinkle formation in film by varying composition and deposition condition, and further implement the optimized structure for solar cells, achieving 23% efficiency. [ABSTRACT FROM AUTHOR]

This study reports the aging effect of a perovskite precursor solution on the photovoltaic performance of perovskite solar cells. The precursor solution is aged at different temperatures of 4, 25 (room temperature), and 65 °C. Power conversion efficiency (PCE) is found to depend on the aging condition. Average PCE increases with aging time, where optimal aging time for best the PCE decreases with aging temperature. Average PCE of 17.29% obtained from a 24 h aged solution at 4 °C is higher than that of 16.48% from a nonaged fresh solution. At 25 °C, a 2–4 h aged solution yields highest PCE of 17.41%. The aging effect is more accelerated at 65 °C, where the best PCE of around 17.10% is achieved from the solution aged for 1.5–2 h. It is commonly observed that photocurrent density is substantially influenced by aging time, while voltage is less affected. Fill factor declines with aging time regardless of aging temperature. Iodoplumbate PbI2S4 (S = solvent) formed in the precursor solution increases its concentration, as aging time increases at a given temperature, which is beneficial for improving photovoltaic performance. No aging effect is found for excess MAI or PbI2 due to initially formed sufficient iodoplumbate. [ABSTRACT FROM AUTHOR]

Abstract: High‐efficiency perovskite solar cells are generally fabricated by using highly pure (>99.99 %) PbI2 mixed with an organic iodide in polar aprotic solvents. However, the use of such an expensive chemical may impede progress toward large‐scale industrial applications. Here, we report on the synthesis of perovskite powders by using inexpensive low‐grade (99 %) PbI2 and on the photovoltaic performance of perovskite solar cells prepared from a powder‐based single precursor. Pure APbI3 [A=methylammonium (MA) or formamidinium (FA)] perovskite powders were synthesized by treating low‐grade PbI2 with MAI or FAI in acetonitrile at ambient temperature. The structural phase purity was confirmed by X‐ray diffraction. The solar cell with a MAPbI3 film prepared from the synthesized perovskite powder demonstrated a power conversion efficiency (PCE) of 17.14 %, which is higher than the PCE of MAPbI3 films prepared by using both MAI and PbI2 as precursors (PCE=13.09 % for 99 % pure PbI2 and PCE=16.39 % for 99.9985 % pure PbI2). The synthesized powder showed better absorption and photoluminescence, which were responsible for the better photovoltaic performance. For the FAPbI3 powder, a solution with a yellow non‐perovskite δ‐FAPbI3 powder synthesized at room temperature was found to lead to a black perovskite film, whereas a solution with the black perovskite α‐FAPbI3 powder synthesized at 150 °C was not transformed into a black perovskite film. The α↔δ transition between the powder and film was assumed to correlate with the difference in the iodoplumbates in the powder‐dissolved solution. An average PCE of 17.21 % along with a smaller hysteresis [ΔPCE=PCEreverse−PCEforward)=1.53 %] was demonstrated from the perovskite solar cell prepared by using δ‐FAPbI3 powder; this PCE is higher than the average PCE of 17.05 % with a larger hysteresis (ΔPCE=2.71 %) for a device based on a conventional precursor solution dissolving MAI with high‐purity PbI2. The smaller hysteresis was indicative of fewer defects in the resulting FAPbI3 film prepared by using the δ‐FAPbI3 powder. [ABSTRACT FROM AUTHOR]

Organic -- inorganic halide perovskite is believed to be a potential candidate for high efficiency solar cells because power conversion efficiency (PCE) was certified to be more than 22%. Nevertheless, mismatch of PCE due to current density (J) -- voltage (V) hysteresis in perovskite solar cells is an obstacle to overcome. There has been much lively debate on the origin of J -- Vhysteresis; however, effective methodology to solve the hysteric problem has not been developed. Here we report a universal approach for hysteresis-free perovskite solar cells via defect engineering. A severe hysteresis observed from the normal mesoscopic structure employing TiO[sub 2] and spiro-MeOTAD is almost removed or does not exist upon doping the pure perovskites, CH[sub 3]NH[sub 3]PbI[sub 3] and HC(NH[sub 2])[sub 2]PbI[sub 3], and the mixed cation/anion perovskites, FA[sub 0.85]MA[sub 0.15]PbI[sub 2.55]Br[sub 0.45] and FA[sub 0.85]MA[sub 0.1]Cs[sub 0.05]PbI[sub 2.7]Br[sub 0.3], with potassium iodide. Substantial reductions in low-frequency capacitance and bulk trap density are measured from the KI-doped perovskite, which is indicative of trap-hysteresis correlation. A series of experiments with alkali metal iodides of LiI, NaI, KI, RbI and CsI reveals that potassium ion is the right element for hysteresis-free perovskite. Theoretical studies suggest that the atomistic origin of the hysteresis of perovskite solar cells is not the migration of iodide vacancy but results from the formation of iodide Frenkel defect. Potassium ion is able to prevent the formation of Frenkel defect since K[sup +] energetically prefers the interstitial site. A complete removal of hysteresis is more pronounced at mixed perovskite system as compared to pure perovskites, which is explained by lower formation energy of K interstitial (-0.65 V for CH[sub 3]NH[sub 3]PbI[sub 3] vs -1.17 V for mixed perovskite). The developed KI doping methodology is universally adapted for hysteresis-free perovskite regardless of perovskite composition and device structure. [ABSTRACT FROM AUTHOR]

Anomalous current–voltage (J–V) hysteresis in perovskite (PSK) solar cell is open to dispute, where hysteresis is argued to be due to electrode polarization, dipolar polarization, and/or native defects. However, a correlation between those factors and J–V hysteresis is hard to be directly evaluated because they usually coexist and are significantly varied depending on morphology and crystallinity of the PSK layer, selective contacts, and device architecture. In this study, without changing morphology and crystallinity of PSK layer in a planar heterojunction structure employing FA0.9Cs0.1PbI3, a correlation between J–V hysteresis and trap density is directly evaluated by means of thermally induced PbI2 regulating trap density. Increase in thermal annealing time at a given temperature of 150 °C induces growth of PbI2 on the PSK grain surface, which results in significant reduction of nonradiative recombination. Hysteresis index is reduced from 0.384 to 0.146 as the annealing time is increased from 5 to 100 min due to decrease in the amplitude of trap-mediated recombination. Reduction of hysteresis by minimizing trap density via controlling thermal annealing time leads to the stabilized PCE of 18.84% from the normal planar structured FA0.9Cs0.1PbI3 PSK solar cell. [ABSTRACT FROM AUTHOR]