Abstract
Defects from grain interiors and boundaries of perovskite films cause significant nonradiative recombination energy loss, and thus perovskite films with controlled crystallinity and large grains is critical for improvement of both photovoltaic performance and stability for perovskite-based solar cells. Here, a methylamine (MA0) gas-assisted crystallization method is developed for fabrication of methylammonium lead iodide (MAPbI3) perovskite films. In the process, the perovskite film is formed via controlled release of MA0 gas molecules from a liquid intermediate phase MAPbI3·xMA0. The resulting perovskite film comprises millimeter-sized grains with (110)-uniaxial crystallographic orientation, exhibiting much low trap density, long carrier lifetime, and excellent environmental stability. The corresponding perovskite solar cell exhibits a power conversion efficiency (PCE) of ~ 21.36%, which is among the highest reported for MAPbI3-based devices. This method provides important progress towards the fabrication of high-quality perovskite thin films for low-cost, highly efficient and stable perovskite solar cells.
Highlights
Defects from grain interiors and boundaries of perovskite films cause significant nonradiative recombination energy loss, and perovskite films with controlled crystallinity and large grains is critical for improvement of both photovoltaic performance and stability for perovskite-based solar cells
In order to improve the quality of the perovskite films, some effective methods have been reported by using various solution processing techniques, such as solvent engineering[28,29], solvent annealing[30], hot casting[31], intramolecular exchange[32,33], and additive-assisted process[27,34,35]
When a raw MAPbI3 thin film is exposed to CH3NH2 (MA0) gas source at room temperature (RT), a liquid intermediate MAPbI3·xMA0 is quickly formed through uptake of the MA0 gas molecules, where the equilibrium is built, as shown below: MAPbl[3] Á xMA0ð1Þ"MAPbl3ðsÞ þ xMA0ðgÞ
Summary
Defects from grain interiors and boundaries of perovskite films cause significant nonradiative recombination energy loss, and perovskite films with controlled crystallinity and large grains is critical for improvement of both photovoltaic performance and stability for perovskite-based solar cells. The high coverage of perovskite film ensures adequate absorption and avoids possible short circuit, and the crystal domains with large grain size and highly orientation are believed to reduce the density of grain boundaries and promote the efficient transport of electrons and holes to their corresponding electrodes. These defects such as the grain boundaries may cause water molecule diffusion and ion migration, deteriorating the device stability[25,26,27]. The perovskite solar cells have been fabricated, yielding a stabilized power conversion efficiency (PCE) of ~21.36% with negligible hysteresis and excellent environmental stability
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