The precise phase control of Cs-Pb-Br derivatives from 3D CsPbBr 3 to 0D Cs 4 PbBr 6 highly determines the photovoltaic performance of all-inorganic CsPbBr 3 perovskite solar cells (PSCs). Herein, the preferred phase conversion from precursor to Cs-Pb-Br derivatives is revealed by theoretically calculating the Gibbs free energies (∆ G ) of various phase conversion processes, allowing for a simplified multi-step solution-processable spin-coating method to hinder the formation of detrimental 0D Cs 4 PbBr 6 phase and enhance the photovoltaic performance of a PSC because of its large exciton binding energy, which is regarded as a recombination center. By further accelerating the interfacial charge extraction with a novel 2D transition metal dichalcogenide ReSe 2 , the hole-free CsPbBr 3 PSC achieves a champion efficiency of 10.67% with an impressive open-circuit voltage of 1.622 V and an excellent long-term stability. This work provides an in-depth understanding on the precise Cs-Pb-Br perovskite phase control and the effect of derivatives on photovoltaic performance of advanced CsPbBr 3 PSCs.
Interface engineering has been proved to be a practical strategy to enhance power conversion efficiency (PCE) and stability of perovskite solar cells. Recently approaches involving ultra-thin layer deposition and vacuum-processing, while improving PCE, increase the processing complexity, and thus the overall cost. In this paper, we demonstrate a high-efficiency inverted planar perovskite solar cell, obtained with a simple wet-chemistry based, room-temperature, and cost-effective process, which synthesizes two interfacial layers: solution processed molybdenum oxide (named s-MoOx) for anode and titanium(IV) oxide bis(2,4-pentanedionate) (TOPD) for cathode buffer layers. Steady-state photoluminescence (PL), time resolved photoluminescence (TRPL) and electrochemical impedance spectroscopy (EIS) are conducted to characterize the charge transport properties, confirming an enhanced charge extraction efficiency and a suppressed charge recombination. In addition, the introduction of the interfacial layers facilities formation of an ohmic contact with the metal electrode, reducing the charge transfer resistance and increasing the FF to as high as 80.7%. The optimized solar cells achieve the best PCE of 16.04% which far exceeds the PCE of devices without these interfacial layers (PCE = 11.2%).
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