Heavy Water Additive in Formamidinium: A Novel Approach to Enhance Perovskite Solar Cell Efficiency

Abstract

Heavy water or deuterium oxide (D2O) comprises deuterium, a hydrogen isotope twice the mass of hydrogen. Contrary to the disadvantages of deuterated perovskites, such as shorter recombination lifetimes and lower/invariant efficiencies, the serendipitous effect of D2O as a beneficial solvent additive for enhancing the power conversion efficiency (PCE) of triple‐A cation (cesium (Cs)/methylammonium (MA)/formaminidium (FA)) perovskite solar cells from ≈19.2% (reference) to 20.8% (using 1 vol% D2O) with higher stability is reported. Ultrafast optical spectroscopy confirms passivation of trap states, increased carrier recombination lifetimes, and enhanced charge carrier diffusion lengths in the deuterated samples. Fourier transform infrared spectroscopy and solid‐state NMR spectroscopy validate the N–H2 group as the preferential isotope exchange site. Furthermore, the NMR results reveal the induced alteration of the FA to MA ratio due to deuteration causes a widespread alteration to several dynamic processes that influence the photophysical properties. First‐principles density functional theory calculations reveal a decrease in PbI6 phonon frequencies in the deuterated perovskite lattice. This stabilizes the PbI6 structures and weakens the electron–LO phonon (Fröhlich) coupling, yielding higher electron mobility. Importantly, these findings demonstrate that selective isotope exchange potentially opens new opportunities for tuning perovskite optoelectronic properties.

High‐Performance Inverted Perovskite Solar Cells with Operational Stability via n‐Type Small Molecule Additive‐Assisted Defect Passivation

“…d) Time-resolved PL spectra of the perovskite films. e) Dark J-V characteristics of the electron-only devices (ITO/SnO 2 /perovskite (without and with Y-Th2)/ [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM)/ZnO/Ag), indicating the V TFL kink point. f) Nyquist plots of the EIS measurements from the devices without and with Y-Th2, and (inset) a circuit diagram of the equivalent circuit model.…”

“…[ 5 ] The inverted structured PSCs also show great promises with advantages such as low‐temperature processability and ionic dopant‐free hole transport layer, which can contribute toward fabricating flexible devices or improving the operational stability. [ 6–14 ] Recently, Zheng et al. reported stable inverted PSCs exhibiting a PCE of 23.0%.…”

Highly Efficient and Stable Perovskite Solar Cells Enabled by Low‐Cost Industrial Organic Pigment Coating

“…However, long‐term stability is widely considered to be one of the major challenges that must be addressed before large scale commercialization of PSCs [5, 6] . Many approaches have been developed during last few years in improving the stability of PSCs, including surface passivation of halide perovskite thin films using various types of materials, such as organic halide salts, [2, 7, 8] polymers, [9–11] organic small molecules, [5, 12–14] low‐dimensional perovskite hybrids, [15, 16] inorganic compounds, [17, 18] and many others [19, 20] . The function of surface passivation is mainly twofold.…”

“…[5,6] Many approaches have been developed during last few years in improving the stability of PSCs,i ncluding surface passivation of halide perovskite thin films using various types of materials,s uch as organic halide salts, [2,7,8] polymers, [9][10][11] organic small molecules, [5,[12][13][14] lowdimensional perovskite hybrids, [15,16] inorganic compounds, [17,18] and many others. [19,20] Thef unction of surface passivation is mainly twofold. Thef irst is in suppressing charge recombination at the interfaces between perovskite and charge transport layers.The second is in increasing device stability by preventing the penetration of degrading agents (i.e.H 2 Oa nd O 2 )i nto the perovskite layer.…”

All‐Vacuum‐Processing for Fabrication of Efficient, Large‐Scale, and Flexible Inverted Perovskite Solar Cells

“…From the UPS results shown in Figure a, the valence bands of the PTAA films were estimated to be −5.2 and −5.31 eV for the spin‐coated and evaporated samples, respectively. By considering the band alignment of the MAPbI 3 perovskite film from the literature, [ 49 ] we plotted the band diagram of the devices with both HTLs, as shown in Figure 4b. We find that the band offset at the PTAA/perovskite interface is only 90 meV for the evaporated PTAA, which is much lower than that of the spin‐coated PTAA with 200 meV band offset.…”