Ultrathin polymeric films for interfacial passivation in wide band-gap perovskite solar cells

Abstract

Wide band-gap perovskite solar cells have the potential for a relatively high output voltage and resilience in a degradation-inducing environment. Investigating the reasons why high voltages with adequate output power have not been realized yet is an underexplored part in perovskite research although it is of paramount interest for multijunction solar cells. One reason is interfacial carrier recombination that leads to reduced carrier lifetimes and voltage loss. To further improve the Voc of methylammonium lead tri-bromide (MAPbBr3), that has a band-gap of 2.3 eV, interface passivation technique is an important strategy. Here we demonstrate two ultrathin passivation layers consisting of PCBM and PMMA, that can effectively passivate defects at the TiO2/perovskite and perovskite/spiro-OMeTAD interfaces, respectively. In addition, perovskite crystallization was investigated with the established anti-solvent method and the novel flash infrared annealing (FIRA) with and without passivation layers. These modifications significantly suppress interfacial recombination providing a pathway for improved VOC’s from 1.27 to 1.41 V using anti solvent and from 1.12 to 1.36 V using FIRA. Furthermore, we obtained more stable devices through passivation after 140 h where the device retained 70% of the initial performance value.

Review of Interface Passivation of Perovskite Layer

“…After 22 d in air, its PCE remained at above 95% of its initial efficiency and it managed to withstand more than 25 h of continuous thermal stress at 85 °C [ 110 ]. Although some materials do not form a chemical reaction with perovskite materials, PCBM and PMMA have been successfully used to passivate defects in perovskites [ 111 , 112 , 114 , 115 ]. Small-sized passivation molecules can be spontaneously distributed in the grain boundary to enhance the passivation effect of the grain boundary defects of hybrid perovskites [ 48 , 58 , 100 , 116 , 117 ].…”

Physical Passivation of Grain Boundaries and Defects in Perovskite Solar Cells by an Isolating Thin Polymer

“…20,25 The combination of PMMA with phenyl-C 61 -butyric acid methyl ester (PCBM) to improve the conductivity of the interlayer compound has also been studied. 20,21,23,24 Several authors have proposed theories for the mechanism behind the performance improvement caused by these interlayers. The conformal coating of thin layers over the perovskite and the passivation of surface defects has been proposed.…”

Accounting for Optical Generation in the Quasi-Neutral Regions of Perovskite Solar Cells

“…2) Perovskite precursor solution and film preparation: A MAPbBr 3 solution was prepared from a precursor solution containing MABr and PbBr 2 (1.4 M) in anhydrous DMF:DMSO 3:1 (v:v). MAPbBr 3 films were prepared by the flash infrared annealing (FIRA), which include the spincoating of the perovskite solution in a single step at 4000 rpm for 10 s [23]- [29]. The substrates were then IR irradiated for 1.4 s in the FIRA oven and were kept there for 20 additional seconds before removal and cooling within several min.…”