Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (
The surface composition of perovskite films is very sensitive to film processing and can deviate from the optimal, which generates unfavorable defects and results in efficiency loss in solar cells and slow response speed in photodetectors. An argon plasma treatment is introduced to modify the surface composition by tuning the ratio of organic and inorganic components as well as defect type before deposition of the passivating layer. It can efficiently enhance the charge collection across the perovskite–electrode interface by suppressing charge recombination. Therefore, perovskite solar cells with argon plasma treatment yield enhanced efficiency to 20.4% and perovskite photodetectors can reach their fastest respond speed, which is solely limited by the carrier mobility.
more » « less- Award ID(s):
- 1538893
- NSF-PAR ID:
- 10049402
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 30
- Issue:
- 9
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract N ,N ‐bis(4‐methoxyphenyl) aniline) (PT‐TPA) which can effectively p‐dope the surface of FAx MA1−x PbI3(FA: HC(NH2)2; MA: CH3NH3) perovskite films is reported. The intermolecular charge transfer property of PT‐TPA forms a stabilized resonance structure to accept electrons from perovskites. The doping effect increases perovskite dark conductivity and carrier concentration by up to 4737 times. Computation shows that electrons in the first two layers of octahedral cages in perovskites are transferred to PT‐TPA. After applying PT‐TPA into perovskite solar cells, the doping‐induced band bending in perovskite effectively facilitates hole extraction to hole transport layer and expels electrons toward cathode side, which reduces the charge recombination there. The optimized devices demonstrate an increased photovoltage from 1.12 to 1.17 V and an efficiency of 23.4% from photocurrent scanning with a stabilized efficiency of 22.9%. The findings demonstrate that molecular doping is an effective route to control the interfacial charge recombination in perovskite solar cells which is in complimentary to broadly applied defect passivation techniques. -
more » « less
Abstract All‐inorganic lead halide perovskite nanocrystals (NCs) have great optoelectronic properties with promising applications in light‐emitting diodes (LEDs), lasers, photodetectors, solar cells, and photocatalysis. However, the intrinsic toxicity of Pb and instability of the NCs impede their broad applications. Shell‐coating is an effective method for enhanced environmental stability while reducing toxicity by choosing non‐toxic shell materials such as metal oxides, polymers, silica, etc. However, multiple perovskite NCs can be encapsulated within the shell material and a uniform epitaxial‐type shell growth of well‐isolated NCs is still challenging. In this work, lead‐free vacancy‐ordered double perovskite Cs2SnX6(X = Cl, Br, and I) shells are epitaxially grown on the surface of CsPbX3NCs by a hot‐injection method. The effectiveness of the non‐toxic double perovskite shell protection is demonstrated by the enhanced environmental and phase stability against UV illumination and water. In addition, the photoluminescence quantum yields (PL QYs) increase for the CsPbCl3and CsPbBr3NCs after shelling because of the type I band alignment of the core/shell materials, while enhanced charge transport properties obtained from CsPbI3/Cs2SnI6core/shell NCs are due to the efficient charge separation in the type II core/shell band alignment.
-
The remarkable optoelectronic properties of metal halide perovskites have generated intense research interest over the last few years. The ability to control and manipulate the crystallisation and stoichiometry of perovskite thin-films has allowed for impressive strides in the development of highly efficient perovskite solar cells. However, being able to effectively modify the interfaces of metal halide perovskites, and to controllably p- or n-type dope the surfaces, may be key to further improvements in the efficiency and long-term stability of these devices. In this study, we use surface doping of the mixed-cation, mixed-halide perovskite FA 0.85 MA 0.15 Pb(I 0.85 Br 0.15 ) 3 (FA – formamidinium; MA – methylammonium) to improve the hole extraction from the perovskite solar cell. By treating the surface of the perovskite film with a strongly oxidizing molybdenum tris(dithiolene) complex, we achieve a shift in the work function that is indicative of p-doping, and a twofold increase in the total conductivity throughout the film. We probe the associated interfacial chemistry through photoelectron and solid-state nuclear magnetic resonance spectroscopies and confirm that charge-transfer occurs between the perovskite and dopant complex. The resulting p-doped interface constitutes a homojunction with increased hole-selectivity. With charge-selective layers, we show that this surface doping enhances the device performance of perovskite solar cells resulting in steady-state efficiencies approaching 21%. Finally, we demonstrate that a surface treatment with this dopant produces the same effect as the commonly employed additive 4- tert butylpyridine ( t BP), allowing us to achieve “ t BP-free” devices with steady-state efficiencies of over 20%, and enhanced thermal stability as compared to devices processed using t BP. Our findings therefore demonstrate that molecular doping is a feasible route to tune and control the surface properties of metal halide perovskites.more » « less
-
more » « less
Abstract The impact of the bulky‐cation‐modified interfaces on halide perovskite solar cell stability is underexplored. In this work, the thermal instability of the bulky‐cation interface layers used in the state‐of‐the‐art solar cells is demonstrated. X‐ray photoelectron spectroscopy and synchrotron‐based grazing‐incidence X‐ray scattering measurements reveal significant changes in the chemical composition and structure at the surface of these films that occur under thermal stress. The changes impact charge‐carrier dynamics and device operation, as shown in transient photoluminescence, excitation correlation spectroscopy, and solar cells. The type of cation used for surface treatment affects the extent of these changes, where long carbon chains provide more stable interfaces. These results highlight that prolonged annealing of the treated interfaces is critical to enable reliable reporting of performances and to drive the selection of different bulky cations.
-
more » « less
Understanding carrier recombination processes in metal halide perovskites is fundamentally important to further improving the efficiency of perovskite solar cells, yet the accurate recombination velocity at grain boundaries (GBs) has not been determined. Here, we report the determination of carrier recombination velocities at GBs (
S GB) of polycrystalline perovskites by mapping the transient photoluminescence pattern change induced by the nonradiative recombination of carriers at GBs. Charge recombination at GBs is revealed to be even stronger than at surfaces of unpassivated films, with averageS GBreaching 2200 to 3300 cm/s. Regular surface treatments do not passivate GBs because of the absence of contact at GBs. We find a surface treatment using tributyl(methyl)phosphonium dimethyl phosphate that can penetrate into GBs by partially dissolving GBs and converting it into one-dimensional perovskites. It reduces the averageS GBby four times, with the lowestS GBof 410 cm/s, which is comparable to surface recombination velocities after passivation.
