In perovskite solar cells, interfaces play a significant role in determining the device stability and device performance. Here, we introduce a versatile donor–π–acceptor (D–π–A) based organic small molecule (AA1) containing phenothiazine (PTZ) with a long alkyl chain as the donor unit, the vinyl-substituted thiophene moiety as a π bridge, and a rhodanine-(CN)2 moiety as an acceptor unit for the first time, and it was successfully deployed to passivate the defects at the surface and grain boundaries of a dual-cation perovskite absorber. The synthesized organic small molecule was characterized thoroughly using 1H NMR, 13C NMR, FT-IR, UV–vis, CV, TGA, and HRMS studies. The FT-IR spectral analysis and X-ray photoelectron spectroscopy (XPS) analysis confirm the interaction between the organic small molecule and the perovskite absorber. Simulated electrostatic potential surface (EPS) images obtained through the density functional theory (DFT) study reveal higher electron density over the acceptor unit of AA1, which ensures effective perovskite defect passivation. The formation of high-quality perovskite film with enhanced crystallinity, improved grain size, and band energy level alignment leads to effective charge carrier transport. The dual nature (defect passivation and optimized band energy level alignment) of AA1 passivation increases the surface photovoltage (from ∼100 to ∼155 mV) and reduces the defect density and ideality factor (∼1.94 × 1014 cm–3 from ∼7.1 × 1014 cm–3 and ∼1.64 from ∼1.88, respectively). The nonradiative recombination is suppressed along with reduced hysteresis, which leads to higher open-circuit voltage (1.09 V from 1.05 V) and power conversion efficiency. This work highlights the use of a push–pull small organic molecule which ensures effective passivation of undercoordinated Pb2+ defects and improved power conversion efficiency. The superior hydrophobic nature of the molecule results in device robustness. Finally, this all-in-one molecule wrestles the three major challenges commonly seen in perovskite solar cells, i.e., interface improvement, unhindered charge carrier transport, and device stability.

Fermi level tuning and defect passivation at the electron selective layer (ESL)/perovskite interface has a strong effect on the perovskite solar cell (PSC) device performance. Two strategies are commonly used for passivation, 1) bulk passivation—by adding dopants in the ESL and 2) surface passivation—to suppress the interface dangling bonds using ligands. Herein, a novel dual passivation (bulk and surface) strategy is presented by incorporating a simple molecule cesium iodide (CsI) in the SnO x ESL. Passivation effects using different CsI dopant concentrations (0–10 wt%) in SnO x solution were studied and its beneficial role of defect passivation is discussed in detail. A systematic study revealed that the addition of CsI in the SnO x ESL not only significantly influences the open‐circuit voltage (V oc) and fill factor (FF), but also suppresses the recombination at the interface due to its improved built in surface potential. Lower trap‐filled limit voltage (V TFL), trap density (n t), and diode ideality factor (n id) are observed for the CsI incorporated SnO x ESL as compared with the bare SnO x layer which leads to a power conversion efficiency improvement from 14.3% to 15.4%.

The presence of intrinsic defects in the bulk perovskite absorber and recombination of charge carriers hampers the device performance in perovskite solar cells. To overcome the bulk defects in the formamidinium cesium lead iodide (FACsPbI 3 ) perovskite absorber layer, A-site cation engineering using nitrogen containing heterocyclic aromatic monovalent molecule, glyoxaline iodide/ imidazolium iodide (IAI) is carried out successfully in this study. Even though IAI is a relatively larger aromatic cation, an optimized concentration of codoping in FACsPbI 3 does not destroy the 3D perovskite lattice as evidenced by X-ray diffraction analysis. Binding energy of Pb-4f core-level shifts to lower energy that reveals that the free lone pair of electrons on the nitrogen atom in IAI binds with the undercoordinated Pb 2+ , which results in in situ defect pas-

The higher basicity and uncontrolled defect states in the planar zinc oxide (ZnO) electron selective layer (ESL) cause rapid deprotonation of the perovskite absorber which results in higher interface charge recombination at the perovskite/ESL interface restricting the usage of ZnO as the ESL in perovskite solar cells. In this work, the isoelectric point (IEP) of ZnO was tuned by introducing a manganese (Mn4+) dopant in ZnO for the first time. The higher oxidation state of the Mn dopant reduces the basicity of the doped ZnO ESL and controls the perovskite deprotonation at the Mn:ZnO/perovskite interface. The doping of Mn4+ in ZnO results in the generation of two free electrons causing higher conductivity of Mn:ZnO films. The dual effect of a lower IEP and higher conductivity of the Mn:ZnO film along with its improved n-type behavior results in higher surface photovoltage and reduced trap-filled limited voltage (V TFL), which resulted in a higher open-circuit voltage (V oc) (0.92 to 0.99 V). The negligible PbI2 formation at the Mn:ZnO/perovskite interface, lower leakage current (1 order lower than that of ZnO), and a comparatively reduced diode ideality factor (n id) validate the improvement of perovskite/interface stability. The above-mentioned merits of the Mn-doped ZnO-based ESL improved the mixed-cation perovskite power conversion efficiency from 11.7 to 13.6%, which is ∼15% higher than that of a bare ZnO-based ESL. Furthermore, a considerably improved device stability of over 100 h under high relative humidity condition (RH >70%) was observed for the Mn-doped ZnO ESL without any encapsulation.