Perovskite solar cells have been rapidly developed in the past ten years. It was demonstrated that the interfacial layer plays an important role in device performance of perovskite solar cells. In this study, we report utilization of a photoinitiation-crosslinked zwitterionic polymer, namely dextran with carboxybetaine modified by methacrylate (Dex-CB-MA), as an interfacial layer to improve the film morphology of the CH 3 NH 3 PbI 3 photoactive layer and the interfacial contact between the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole extraction layer and CH 3 NH 3 PbI 3 photoactive layer. It is found that the Dex-CB-MA thin layer forms a better band alignment between the PEDOT:PSS hole extraction layer and CH 3 NH 3 PbI 3 photoactive layer, and improves the crystallization of the CH 3 NH 3 PbI 3 photoactive layer, resulting in efficient charge carrier transport. As a result, perovskite solar cells with the PEDOT:PSS/Dex-CB-MA hole extraction layer exhibit more than 30% enhancement in efficiency and dramatically boosted stability as compared with that with the PEDOT:PSS hole extraction layer. Our studies provide an effective and facile way to fabricate stable perovskite solar cells with high power conversion efficiency.
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Synergistic Effect of Elevated Device Temperature and Excess Charge Carriers on the Rapid Light‐Induced Degradation of Perovskite Solar Cells
With power conversion efficiencies now reaching 24.2%, the major factor limiting efficient electricity generation using perovskite solar cells (PSCs) is their long‐term stability. In particular, PSCs have demonstrated rapid degradation under illumination, the driving mechanism of which is yet to be understood. It is shown that elevated device temperature coupled with excess charge carriers due to constant illumination is the dominant force in the rapid degradation of encapsulated perovskite solar cells under illumination. Cooling the device to 20 °C and operating at the maximum power point improves the stability of CH3NH3PbI3solar cells over 100× compared to operation under open circuit conditions at 60 °C. Light‐induced strain originating from photothermal‐induced expansion is also observed in CH3NH3PbI3, which excludes other light‐induced‐strain mechanisms. However, strain and electric field do not appear to play any role in the initial rapid degradation of CH3NH3PbI3solar cells under illumination. It is revealed that the formation of additional recombination centers in PSCs facilitated by elevated temperature and excess charge carriers ultimately results in rapid light‐induced degradation. Guidance on the best methods for measuring the stability of PSCs is also given.
more » « less- PAR ID:
- 10461205
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 31
- Issue:
- 35
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Despite the rapid progress in solar power conversion efficiency of archetype organic–inorganic hybrid perovskite CH3NH3PbI3‐based solar cells, the long‐term stability and toxicity of Pb remain the main challenges for the industrial deployment, leading to more uncertainties for global commercialization. The poor stabilities of CH3NH3PbI3‐based solar cells may not only be attributed to the organic molecules but also the halides themself, most of which exhibit intrinsic instability under moisture and light. As an alternative, the possibility of oxide perovskites for photovoltaic applications is explored here. The class of lead‐free stable oxide double perovskites A2M(III)M(V)O6(A = Ca, Sr, Ba; M(III) = Sb3+or Bi3+; M(V) = V5+, Nb5+, or Ta5+) is comprehensively explored with regard to their stability and their electronic and optical properties. Apart from the strong stability, this class of double perovskites exhibits direct bandgaps ranging from 0.3 to 3.8 eV. With proper B site alloying, the bandgap can be tuned within the range of 1.0–1.6 eV with optical absorptions as strong as CH3NH3PbI3, making them suitable for efficient single‐junction thin‐film solar cell application.
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Abstract Understanding interfacial reactions that occur between the active layer and charge‐transport layers can extend the stability of perovskite solar cells. In this study, the exposure of methylammonium lead iodide (CH3NH3PbI3) thin films prepared on poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐coated glass to 70% relative humidity (R.H.) leads to a perovskite crystal structure change from tetragonal to cubic within 2 days. Interface‐sensitive photoluminescence measurements indicate that the structural change originates at the PEDOT:PSS/perovskite interface. During exposure to 30% R.H., the same structural change occurs over a much longer time scale (>200 days), and a reflection consistent with the presence of (CH3)2NH2PbI3is detected to coexist with the cubic phase by X‐ray diffraction pattern. The authors propose that chemical interactions at the PEDOT:PSS/perovskite interface, facilitated by humidity, promote the formation of dimethylammonium, (CH3)2NH2+. The partial A‐site substitution of CH3NH3+for (CH3)2NH2+to produce a cubic (CH3NH3)1−
x [(CH3)2NH2]x PbI3phase explains the structural change from tetragonal to cubic during short‐term humidity exposure. When (CH3)2NH2+content exceeds its solubility limit in the perovskite during longer humidity exposures, a (CH3)2NH2+‐rich, hexagonal phase of (CH3NH3)1−x [(CH3)2NH2]x PbI3emerges. These interfacial interactions may have consequences for device stability and performance beyond CH3NH3PbI3model systems and merit close attention from the perovskite research community. -
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Abstract Semiconducting molecules have been employed to passivate traps extant in the perovskite film for enhancement of perovskite solar cells (PSCs) efficiency and stability. A molecular design strategy to passivate the defects both on the surface and interior of the CH3NH3PbI3perovskite layer, using two phthalocyanine (Pc) molecules (
NP ‐SC6‐ZnPc andNP ‐SC6‐TiOPc) is demonstrated. The presence of lone electron pairs on S, N, and O atoms of the Pc molecular structures provides the opportunity for Lewis acid–base interactions with under‐coordinated Pb2+sites, leading to efficient defect passivation of the perovskite layer. The tendency of bothNP ‐SC6‐ZnPc andNP ‐SC6‐TiOPc to relax on the PbI2terminated surface of the perovskite layer is also studied using density functional theory (DFT) calculations. The morphology of the perovskite layer is improved due to employing the Pc passivation strategy, resulting in high‐quality thin films with a dense and compact structure and lower surface roughness. UsingNP ‐SC6‐ZnPc andNP ‐SC6‐TiOPc as passivating agents, it is observed considerably enhanced power conversion efficiencies (PCEs), from 17.67% for the PSCs based on the pristine perovskite film to 19.39% forNP ‐SC6‐TiOPc passivated devices. Moreover, PSCs fabricated based on the Pc passivation method present a remarkable stability under conditions of high moisture and temperature levels. -
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Abstract High‐performance tin‐lead perovskite solar cells (PSCs) are needed for all‐perovskite‐tandem solar cells. However, iodide related fast photodegradation severely limits the operational stability of Sn‐Pb perovskites despite the demonstrated high efficiency and thermal stability. Herein, this work employs an alkylammonium pseudo‐halogen additive to enhance the power conversion efficiency (PCE) and photostability of methylammonium (MA)‐free, Sn‐Pb PSCs. Density functional theory (DFT) calculations reveal that the pseudo‐halogen tetrafluoroborate (BF4−) has strong binding capacity with metal ions (Sn2+/Pb2+) in the Sn‐Pb perovskite lattice, which lowers iodine vacancy formation. Upon combining BF4−with an octylammonium (OA+) cation, the PCE of the device with a built‐in light‐scattering layer is boosted to 23.7%, which represents a new record for Sn‐Pb PSCs. The improved efficiency benefits from the suppressed defect density. Under continuous 1 sun illumination, the OABF4embodied PSCs show slower generation of interstitial iodides and iodine, which greatly improves the device photostability under open‐circuit condition. Moreover, the device based on OABF4retains 88% of the initial PCE for 1000 h under the maximum‐power‐point tracking (MPPT) without cooling.
