Grain Engineering for Perovskite/Silicon Monolithic Tandem Solar Cells with Efficiency of 25.4%

Abstract

Grain engineering through combined MACl and MAH 2 PO 2 additives in perovskite precursors improves the photovoltaic performance of perovskite/silicon tandem cells. MACl increases the grain size of wide-bandgap perovskite films and also produces smooth films. MAH 2 PO 2 suppresses non-radiative recombination sites at grain boundaries. The synergetic effects of MACl and MAH 2 PO 2 further promote grain growth and prolong the carrier recombination lifetime. This enables a power conversion efficiency of 25.4% for a perovskite/silicon tandem device. SUMMARYOrganic-inorganic halide perovskites are promising semiconductors to mate with silicon in tandem photovoltaic cells due to their solution processability and tunable complementary bandgaps. Herein, we show that a combination of two additives, MACl and MAH 2 PO 2 , in the perovskite precursor can significantly improve the grain morphology of wide-bandgap (1.64-1.70 eV) perovskite films, resulting in solar cells with increased photocurrent while reducing the open-circuit voltage deficit to 0.49-0.51 V. The addition of MACl enlarges the grain size, while MAH 2 PO 2 reduces non-radiative recombination through passivation of the perovskite grain boundaries, with good synergy of functions from MACl and MAH 2 PO 2 . Matching the photocurrent between the two subcells in a perovskite/silicon monolithic tandem solar cell by using a bandgap of 1.64 eV for the top cell results in a high tandem V oc of 1.80 V and improved power conversion efficiency of 25.4%.

Μethylammonium Chloride: A Key Additive for Highly Efficient, Stable, and Up‐Scalable Perovskite Solar Cells

“…[74] Strikingly, through synchrotron-based nanoprobe X-ray fluorescence, Luo et al have detected Cl-rich regions along or adjacent to crystal grain boundaries of a MACl-excessive (1 or 2 moles) MAPbI 3 perovskite. [72] Very similar results with lower trap density upon MACl addition in MAPbI 3 perovskites were drawn from space-charge-limited current or impedance spectroscopy measurements. [72] Very similar results with lower trap density upon MACl addition in MAPbI 3 perovskites were drawn from space-charge-limited current or impedance spectroscopy measurements.…”

“…[72] Very similar results with lower trap density upon MACl addition in MAPbI 3 perovskites were drawn from space-charge-limited current or impedance spectroscopy measurements. [64,65,72,76] Remarkably, MAH 2 PO 2 -only additive, which is the product of the reaction of H 3 PO 2 with methylamine, [77] already presented a lower density of defects at grain boundaries in comparison with MACl. [64,65,72,76] Remarkably, MAH 2 PO 2 -only additive, which is the product of the reaction of H 3 PO 2 with methylamine, [77] already presented a lower density of defects at grain boundaries in comparison with MACl.…”

“…[72] The higher <110>-preferred orientations, which exhibit the MAPbI 3 perovskite films by using excess of MACl compared with that from stoichiometric precursors, were recently explained by Lee and coworkers. [72] The higher <110>-preferred orientations, which exhibit the MAPbI 3 perovskite films by using excess of MACl compared with that from stoichiometric precursors, were recently explained by Lee and coworkers.…”

“…[67,71] In any case, we should highlight here the fact that when a second chloride salt (methylammonium acetate, MAH 2 PO 2 , and CsCl) was added in MACl-excessive perovskites, a better passivation effect was observed in comparison with MACl-only additive. [72] Therefore, we believe that the exact effect of MACl in trap passivation should be more elaborated in the future. [72] Therefore, we believe that the exact effect of MACl in trap passivation should be more elaborated in the future.…”

“…[67] Interestingly, very similar results with monolithic films, consisted of grains of 3.6 µm, could be prepared without any anti-solvent nor DMSO, but with the assistance of thermal energy provided during crystallization. [72] Figure 5. The films turned black after spinning, implying that the temperature accelerates the evaporation of DMF and the diffusion speed of MAI to form a MAPbI 3 film which contains impurities such as MACl and MAPbCl 3 .…”