Organic N‐Type Molecule: Managing the Electronic States of Bulk Perovskite for High‐Performance Photovoltaics

Abstract

The power conversion efficiency (PCE) of planar p–i–n perovskite solar cells (pero‐SCs) is commonly lower than that of the n–i–p pero‐SCs, due to the severe nonradiative recombination stemming from the more p‐type perovskite with prevailing electron traps. Here, two n‐type organic molecules, DMBI‐2‐Th and DMBI‐2‐Th‐I, with hydrogen‐transfer properties for the doping of bulk perovskite aimed at regulating its electronic states are synthesized. The generated radicals in these n‐type dopants with high‐lying singly occupied molecular orbitals enable easy transfer of the thermally activated electrons to the MAPbI3 perovskite for the realization of n‐doped perovskites. The n‐doping degree could be further enhanced by using the iodine ionized dopant DMBI‐2‐Th‐I. The doping effect could reduce the electron trap density, increase the electron concentration of the bulk perovskite, and simultaneously improve the surface electronic contact. When the DMBI‐2‐Th‐I‐doped perovskite is used in planar p–i–n pero‐SCs, the nonradiative recombination is significantly suppressed. As a result, the photovoltaic performance improved significantly, as evidenced by an excellent PCE of 20.90% and a robust ambient stability even under high relative humidity. To the best of the knowledge, this work represents the first example where organic n‐type dopants are used to tune the electronic states of a bulk perovskite film for efficient planar p–i–n pero‐SCs.

One‐Source Strategy Boosting Dopant‐Free Hole Transporting Layers for Highly Efficient and Stable CsPbI2Br Perovskite Solar Cells

“…In addition, we also observed that the Pb and I antisite defects exist widely in the grain boundaries of control CsPbI 2 Br as evidenced by the localized electron distribution around the antisite defect site. [ 52 ] In the CsPbI 2 Br‐PT film, however, the electron distribution was effectively delocalized by the passivation of gradient‐attached PBDB‐T molecules, where the Lewis base S atoms can bond to Pb atoms to passivate the under‐coordinated Pb 2+ . [ 50 ] This result was also confirmed by X‐ray photoelectron spectroscopy measurements, where the Pb 4f peak of the CsPbI 2 Br‐PT film shifted toward a lower binding energy compared to the control CsPbI 2 Br film, suggesting coordination bonds formed between PBDB‐T and under‐coordinated Pb 2+ ions in CsPbI 2 Br (Figure S17, Supporting Information).…”

High‐Polarizability Organic Ferroelectric Materials Doping for Enhancing the Built‐In Electric Field of Perovskite Solar Cells Realizing Efficiency over 24%

“…[10] In this process, the electrons or holes are likely to be captured or trapped by the defects through Coulombic interactions, resulting in nonradiative recombination, which causes unexpected energy losses in the pero-SCs. [11] Because of the polycrystalline nature of the solution-processed perovskite film, it is difficult to suppress the defects, even via crystal growth regulation, [12] carrier-concentration manipulation, [13] and defect passivation strategies. [14] The BEF in pero-SCs is considered to be the driving force behind transporting and extracting the charge carriers, prior to their capture by the defects or accumulation at the interfaces.…”

p-Type molecular doping by charge transfer in halide perovskite

“…13,14 Yet, more homogeneous perovskite doping with molecular dopants is still in its infancy, showing only modest conductivity improvements. [15][16][17][18] Doping of a particular perovskite host through charge transfer requires appropriate selection of the molecular dopant. p-Type doping can occur if the lowest unoccupied molecular orbital (LUMO) of the molecular dopant lies near or below the valence band maximum (VBM) of the perovskite host.…”