Fabrication and characterization of triple-cation perovskite solar cells

Abstract

Presently, triple-cation perovskite solar cells have been appealing due to the outstanding power conversion efficiency (PCE). In this work, the Cs0.03(FAxMA1-x)0.97Pb(IyBr1-y)3 triple-cation perovskite solar cells fabricated by two-step deposition method were studied by varying the content of halide ions (Br and I) and the cation ratios of FA and MA. The results showed that the insertion of Br improved open-circuit voltage due to broader band gap. In case of MAPbI3-based devices, the PCE was also increased with the addition of Br. However, the FAPbI3-based devices were inferior to MAPbI3-based devices resulting from poor quality perovskite layer and the non-photoactive structure of FAPbI3. To fabricate the FAPbI3-based devices, more procedures were needed to obtain high performance. Two-step deposition method with perovskite seeds was employed to improve the photovoltaic performance of FAPbI3-based devices. This process was slightly modified from conventional two-step deposition methods by adding small amount of perovskite seed precursor into PbI2 solution and the concentration of the perovskite seeds in PbI2 solution was varied in this study. The SEM images indicated that the FAPbI3-based films of the new method were more compact and denser than that of the conventional method which improved surface coverage causing the better contact between perovskite layer and hole transport layer. The average PCEs were enhanced from 5.2% to 11.9% when the fabrication method changed from the conventional method to two-step deposition method with 7% v/v seeding concentration due to the favorable of perovskite seeds for crystal formation and improved contact of photoactive layer and hole transport layer. The performance of the seeding method could be improved by using proper amount of chlorobenzene as an anti-solvent. For instance, the average PCEs of 14% v/v seeding concentration was risen from 10.8% to 14.3% when the applied anti-solvent was changed from 50 µl to 30 µl. Besides, the photovoltaic performance of triple-cation perovskite solar cells from both methods and the standard MAPbI3 were compared. It was found that the grain size was not an impact factor to determine the performance of devices because the average PCEs of seeded devices were around 13-14% as much as the standard devices and MAPbI3-based devices, although the grain size of FAPbI3- and MAPbI3-based devices were noticeably different.