skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: The charge carrier dynamics, efficiency and stability of two-dimensional material-based perovskite solar cells
Perovskites have been firmly established as one of the most promising materials for third-generation solar cells. There remain several great and lingering challenges to be addressed regarding device efficiency and stability. The photovoltaic efficiency of perovskite solar cells (PSCs) depends drastically on the charge-carrier dynamics. This complex process includes charge-carrier generation, extraction, transport and collection, each of which needs to be modulated in a favorable manner to achieve high performance. Two-dimensional materials (TDMs) including graphene and its derivatives, transition metal dichalcogenides ( e.g. , MoS 2 , WS 2 ), black phosphorus (BP), metal nanosheets and two-dimensional (2D) perovskite active layers have attracted much attention for application in perovskite solar cells due to their high carrier mobility and tunable work function properties which greatly impact the charge carrier dynamics of PSCs. To date, significant advances have been achieved in the field of TDM-based PSCs. In this review, the recent progress in the development and application of TDMs ( i.e. , graphene, graphdiyne, transition metal dichalcogenides, BP, and others) as electrodes, hole transporting layers, electron transporting layers and buffer layers in PSCs is detailed. 2D perovskites as active absorber materials in PSCs are also summarized. The effect of TDMs and 2D perovskites on the charge carrier dynamics of PSCs is discussed to provide a comprehensive understanding of their optoelectronic processes. The challenges facing the PSC devices are emphasized with corresponding solutions to these problems provided with the overall goal of improving the efficiency and stability of photovoltaic devices.  more » « less
Award ID(s):
1914713 1914562 1803495
PAR ID:
10142694
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Chemical Society Reviews
Volume:
48
Issue:
18
ISSN:
0306-0012
Page Range / eLocation ID:
4854 to 4891
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract Formamidinium (FA)‐based lead iodide perovskites have emerged as the most promising light‐absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the phase‐instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA‐based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA‐based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but also enhances the charge‐carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment‐theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000‐h storage under ambient conditions. 
    more » « less
  2. Efficient charge collection is critical in large area (quasi-) planar configuration perovskite solar cells (PSCs) as the cell operation relies on the diffusion of photo-generated charge carriers to charge collector layers. Many defects/traps in the polycrystalline perovskite absorber layer strongly affect the charge collection efficiency because the 2D-like top charge collection layer barely penetrates into the 3D grain boundaries in the perovskite layer to efficiently collect the charge carrier. Inspired by blood capillaries for efficient mass exchange, a charge-collection nano-network for efficient charge collection was incorporated into the perovskite absorber using low-cost, stable amino-functionalized graphene (G-NH 2 ). The integration of such an unprecedented structure enables very efficient charge collection, leading to the significant enhancement of the power conversion efficiency of 1 × 1 cm 2 MAPbI 3 PSCs from 14.4 to 18.7% with higher reproducibility, smaller hysteresis and enhanced stability. The physicochemical mechanisms underlying the role of this nano charge-collection nano-network in boosting the charge collection in PSCs are elucidated comprehensively, using a combined experimental and theoretical approach, pointing to a new direction towards up-scaling of high-efficiency PSCs. 
    more » « less
  3. Abstract Typical lead‐based perovskites solar cells show an onset of photogeneration around 800 nm, leaving plenty of spectral loss in the near‐infrared (NIR). Extending light absorption beyond 800 nm into the NIR should increase photocurrent generation and further improve photovoltaic efficiency of perovskite solar cells (PSCs). Here, a simple and facile approach is reported to incorporate a NIR‐chromophore that is also a Lewis‐base into perovskite absorbers to broaden their photoresponse and increase their photovoltaic efficiency. Compared with pristine PSCs without such an organic chromophore, these solar cells generate photocurrent in the NIR beyond the band edge of the perovskite active layer alone. Given the Lewis‐basic nature of the organic semiconductor, its addition to the photoactive layer also effectively passivates perovskite defects. These films thus exhibit significantly reduced trap densities, enhanced hole and electron mobilities, and suppressed illumination‐induced ion migration. As a consequence, perovskite solar cells with organic chromophore exhibit an enhanced efficiency of 21.6%, and substantively improved operational stability under continuous one‐sun illumination. The results demonstrate the potential generalizability of directly incorporating a multifunctional organic semiconductor that both extends light absorption and passivates surface traps in perovskite active layers to yield highly efficient and stable NIR‐harvesting PSCs. 
    more » « less
  4. 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
  5. Conjugated molecules have been typically utilized as either hole or electron extraction layers to boost the device performance of perovskite solar cells (PSCs), formed from three-dimensional (3D) perovskites, due to their high charge carrier mobility and electrical conductivity. However, the passivating role of conjugated molecules in creating two-dimensional (2D) perovskites has rarely been reported. In this study, we report novel conjugated aniline 3-phenyl-2-propen-1-amine (PPA) based 2D perovskites and further demonstrate efficient and stable PSCs containing a (PPA) x (MAPbI 3 ) 1− x /MAPbI 3 bilayer thin film (where MA is CH 3 NH 3 + ). The (PPA) x (MAPbI 3 ) 1− x /MAPbI 3 bilayer thin film possesses superior crystallinity and passivated trap states, resulting in enhanced charge transport and suppressed charge carrier recombination compared to those of a 3D MAPbI 3 thin film. As a result, PSCs containing the (PPA) x (MAPbI 3 ) 1− x /MAPbI 3 bilayer thin film exhibit a power conversion efficiency (PCE) of 21.98%, which is approximately a 25% enhancement compared to that of the MAPbI 3 thin film. Moreover, un-encapsulated PSCs containing the (PPA) x (MAPbI 3 ) 1− x /MAPbI 3 bilayer thin film retain 50% of their initial PCE after 1200 hours in an ambient atmosphere (25 °C, and 30 ± 10 humidity), whereas PSCs with the 3D MAPbI 3 thin film show significant degradation after 100 hours and a degradation of more than 50% of their original PCE after 500 hours. These results demonstrate that the incorporation of conjugated molecules as organic spacer cations to create 2D perovskites on top of 3D perovskites is an effective way to approach high-performance PSCs. 
    more » « less