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Understanding the device kinetics occurring in the bulk and charge selective layers is vital for optimizing the performance of perovskite solar cells (PSCs) and their development. We studied planar PSCs with and without hole transport layer (HTL) and measured hysteresis free power conversion efficiency of 16.23% with poly(3-hexylthiophene) [P3HT] as HTL, while the PSCs without HTL showed significant hysteresis. We investigated a comprehensive electrical response of the PSCs. The bias-dependent electrochemical impedance spectroscopy (EIS) revealed the appearance of the negative capacitance in the low-frequency regime. The modification of the low-frequency PSCs response accompanied by a further decrease in recombination resistance is due to the interfacial interactions between the migrating ions and the metal contact. The doped and undoped P3HT layers impeded this interaction which explains the absence of the negative capacitance at lower applied voltages. Our investigation provides an understanding of the physical processes behind the negative capacitance.

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A donor-acceptor small organic molecule, p-N,N-dimethyl-amino-benzylidene-malononitrile (DABMN), has been synthesized and successfully prepared in thin films using spin coating technique. The thin film of DABMN exhibited semiconductor behavior with an optical band gap of about 2.27 eV. The photoluminescence spectrum was exhibited a strong red emission. The energy levels of lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) were determined by experimental calculation from cyclic voltammetry. The electrical performance of the ITO/DABMN/Al structure device was evaluated through current-voltage characteristics and showed a typical Schottky diode behavior with good charge mobility. The charge density associated with the DABMN film was calculated from the capacitance-voltage measurements.

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