Facile Method to Reduce Surface Defects and Trap Densities in Perovskite Photovoltaics

Abstract

Owing to improvements in film morphology, crystallization process optimization, and compositional design, the power conversion efficiency of perovskite solar cells has increased from 3.8 to 22.1% in a period of 5 years. Nearly defect-free crystalline films and slow recombination rates enable polycrystalline perovskite to boast efficiencies comparable to those of multicrystalline silicon solar cells. However, volatile low melting point components and antisolvent treatments essential for the processing of dense and smooth films often lead to surface defects that hamper charge extraction. In this study, we investigate methylammonium bromide (MABr) surface treatments on perovskite films to compensate for the loss of volatile cation during the annealing process for surface defect passivation, grain growth, and a bromide-rich top layer. This facile method did not change the phase or bandgap of perovskite films yet resulted in a significant increase in the open circuit voltages of devices. The devices with 10 mM MABr treatment show 2% improvement in absolute power conversion efficiency over the control sample.

Mixed 3D–2D Passivation Treatment for Mixed‐Cation Lead Mixed‐Halide Perovskite Solar Cells for Higher Efficiency and Better Stability

“…[9,17,27] Upon deposition of the mixture of FAI and iBAI solution on the perovskite surface, prominent changes can be observed: 1) the bright white grains on the surface disappeared; 2) surface morphology is changed as the iBAI content increases. [8,9,17] The formation of a surface layer on the MP50-treated sample is confirmed by cross-section SEM imaging (Figure 2h), showing a continuous film with finer grains formed on top of the 3D perovskite which has much larger grains. Pinholes occasionally appear in this surface layer (Figure 2b and Figure S3 (Supporting Information)).…”

“…If the total concentration of the MP precursor solutions is higher than the 60 × 10 −3 m (molarity of the excess PbI 2 ), device performance after MP treatment deteriorates (see Figure S1 in the Supporting Information). [7,8,11] While V OC of all devices with MP treatment are higher than the reference cells, the short-circuit current density (J SC ) and FF are influenced noticeably by the iBAI to FAI ratio. Detailed description of the device fabrication procedure is provided in the Supporting Information.…”

“…This is also supported by the results of time-resolved PL decay measurements ( Figure S8b, Supporting Information). [7,8,11] We note that the nature of the surface defects on the bulk ( formation of the top passivation layer. These results show the effectiveness of the passivation layers in reducing the number of surface defects or/and mitigating the effectiveness of the surface defects as charge-carrier trap sites.…”

“…These results show the effectiveness of the passivation layers in reducing the number of surface defects or/and mitigating the effectiveness of the surface defects as charge-carrier trap sites. [8,14] Considering the PL spectrum of the reference sample, the emissive states forming similar PL peak emission in the MP-treated samples are mainly those originated from the bottom bulk perovskite, allowing the assessment of the impact of the treatment layers on the perovskite absorber bulk in addition to its surface. [9] Also, new and possibly more benign trap sites with different properties could be created near the surface of the (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 perovskite bulk due to potential infiltration of the MP precursor solution and subsequent chemical reaction.…”

CH3NH3Br Additive for Enhanced Photovoltaic Performance and Air Stability of Planar Perovskite Solar Cells prepared by Two‐Step Dipping Method

“…Moreover, some large crystal grains increase in size and the film becomes more compact compared with the one without MABr additive. In principle, the crystal growth rate of the perovskite film could be slowed down by the added Br − anions, thereby leading to the formation of large crystal grains and a high‐quality perovskite film . Yang et al.…”