Strategies on narrow-bandgap tin-lead perovskites toward high-efficiency photovoltaic devices

Abstract

Photovoltaic devices, including photodetectors (PDs) and solar cells, play important roles in various applications, such as optical communication, biomedical imaging, transportation, global lighting system and power supply. Conventional photovoltaic devices mainly rely on inorganic semiconductors, which are mechanically fragile, pricey, and require high-temperature/vacuum procedures. Therefore, it is very essential to develop novel semiconductors based photovoltaic devices with easy fabrication, low cost, flexibility compatibility and energy conservation. In this thesis, we achieve goals as follows: Firstly, we demonstrate a double-side crystallization tuning approach with space-restricted low-temperature annealing to grow the tin-lead perovskite thick film (over 1 μm) for near-infrared (NIR) photodetection. Through the controllable crystallization manner of space-restricted low-temperature annealing, smooth, pinhole-/void-free tin-lead perovskite thick film with increased crystallinity, preferred stacking pattern as well as reduced defects are achieved. Finally, tin-lead perovskite NIR PDs achieve flat and high EQE of about 80% among 760-900 nm, notable responsivity of 0.53 A W-1 and specific detectivity (D*) of 6 × 1012 Jones at 940 nm. Secondly, we introduce Sn(SCN)2 additives into tin-lead perovskites for high-detectivity NIR PDs. Surprisingly, the Sn(SCN)2 additive presents a unique double-sided surface-preferred distribution within the perovskite film, which locate most at bottom and top surfaces, and tiny minority inside the film. The tailored tin-lead perovskites with distinctive additive distribution achieves largely improved morphology and antioxidation ability. Consequently, the optimized tin-lead perovskite NIR PDs obtain a peak responsivity of 0.57 A W-1 and a D* of 8.48 × 1012 Jones at 910 nm, a large linear dynamic range of 213 dB, accompanied by outstanding lifetime of 2300 h. Thirdly, we propose a synergistic integration strategy by simultaneously employing reducing agent and in-situ surface passivation in MA-free tin-lead perovskites to increase the performance of HTL-free MA-free tin-lead perovskite solar cells (PSCs). The synergistic integration strategy facilitates to prevent the Sn2+ oxidation as well as passivate defects. Additionally, the energy-level alignment is largely improved through forming tin-lead perovskite films with synergistic integration strategy and treating the ITO substrate with UV-Ozone. Consequently, HTL-free MA-free tin-lead PSCs exhibit a highest PCE of 17.4%, and a greatly improved stability of keeping the PCE well at beginning 200 h, and maintaining 81% of initial value after aging in the air for 480 h. Finally, we employ chlorogenic acid (CGA) reducing agent in the tin-lead perovskites to achieve significantly enhanced NIR photodetection. Particularly, the introduced CGA additive would interact with fundamental SnF2 additive to form a CGA-SnF2 complex so that create a top-encased protection layer for the bulk perovskites. Contributed by the functional groups of CGA and the unique protection layer, optimized tin-lead perovskites present improved energy-level alignment, enhanced antioxidation, and increased defects suppression and passivation. As a result, the self-powered NIR PDs with optimized tin-lead perovskites exhibit a high EQE of around 76% as well as a remarkable D* of 2× 1013 Jones at 940 nm, with significantly prolonged stability of keeping 96% of initial photocurrent after 127 days.