Enhancing the Open-Circuit Voltage of Perovskite Solar Cells by Embedding Molecular Dipoles within Their Hole-Blocking Layer

Butscher, Julian F.; Intorp, Sebastian N.; Kreß, Joshua; An, Qingzhi; Hofstetter, Yvonne J.; Hippchen, Nikolai; Paulus, Fabian; Bunz, Uwe H. F.; Tessler, Nir; Vaynzof, Yana

doi:10.1021/acsami.9b18757

Cited by 32 publications

(29 citation statements)

References 59 publications

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“…It can be seen that the (WF = 4.42 eV) of M‐PTAA is ≈100 meV smaller than that of R‐PTAA (WF = 4.52 eV), which corresponds to a smaller built‐in potential in a photovoltaic (PV) device. [ 31 ] On the other hand, the energy difference (Δ E ) between the Fermi level (FL) and the highest occupied molecular orbital (HOMO) level of M‐PTAA is 0.65 eV, which is 150 meV larger than that of R‐PTAA (0.5 eV). The increase in Δ E comes from the electron injection from ITO to the HOMO level of PTAA, which annihilates the free carriers in PTAA and increases its resistance.…”

Section: Resultsmentioning

confidence: 99%

Facile Physical Modifications of Polymer Hole Transporting Layers for Efficient and Reproducible Perovskite Solar Cells with Fill Factor Exceeding 80%

et al. 2020

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The hole transport materials that interact with the indium tin oxide (ITO) surface can be processed into monomolecular layers (MLs), which often exhibit different surface and electronic properties than their thin‐film counterparts. Herein, it is found that poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) films (R‐PTAA) can be easily processed into ML (M‐PTAA) due to the van der Waals interaction between ITO and PTAA. However, compared with R‐PTAA, the work function (WF) and conductivity of M‐PTAA are simultaneously reduced by the charge transfer at the ITO/PTAA interface. To address this issue, a modified monomolecular layer strategy (m‐MLS) is developed, where a small amount of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) is introduced to enhance the interaction force between ITO and PTAA. PTAA treated by m‐MLS (F‐PTAA) has a hydrophilic physical surface, closely matching electronic energy level with the perovskite layer and smaller bulk resistance. As a result, the efficiency and reproducibility of perovskite solar cells (PSCs) are substantially improved. PSCs based on F‐PTAA demonstrated the highest power conversion efficiency (PCE) of 19.7% with a fill factor of over 80%. This study inspires the development of novel interface modification materials, and provides a simple and convenient direction for the fabrication of high‐performance and reproducible inverted PSCs with high fill factors.

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Section: Resultsmentioning

confidence: 99%

Facile Physical Modifications of Polymer Hole Transporting Layers for Efficient and Reproducible Perovskite Solar Cells with Fill Factor Exceeding 80%

et al. 2020

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“…[118] Interfacial engineering can serve different purposes such as passivation of interfacial defects, [119,120] suppression of ion migration [121,122] or interfacial reactions, [123][124][125] and compensation of unsatisfactory energetic alignment. [126,127] Many of these strategies can be adopted to thermally evaporated perovskites, so long as the materials used can be deposited by thermal evaporation. Potentially, thermally deposited devices might even hold an advantage, due to the possibility to deposit complex multilayered devices without limitations such as solvent orthogonality that restrict the possible combinations of materials that can be deposited from solution.…”

Section: Photovoltaic Performancementioning

confidence: 99%

The Future of Perovskite Photovoltaics—Thermal Evaporation or Solution Processing?

Vaynzof

2020

Advanced Energy Materials

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single solution, which is deposited onto the substrate, following by a thermal annealing step. [6,7] While this approach is very simple and is still relatively common for certain perovskite compositions, [8,9] the perovskite precursors maybe undergo various chemical reactions in solution, which will influence both the resulting film and the performance of photovoltaic devices. [10] An alternative approach, especially popular in the early days of perovskite research, is the two-step approach, in which one of the precursors is deposited first, followed by the deposition of a second precursor and thermal annealing. [11] Most commonly, the first precursor (e.g., lead iodide, PbI 2) is deposited by spin-coating, while the second one (e.g., methylammonium iodide, MAI) can be deposited by dipping the sample into a solution, [12] or by spin-coating on top of the first layer. [13] For a time, devices fabricated using the two-step method showed higher performance than those made using the one-step, [14] but the situation drastically changed upon the introduction of the solvent engineering approach, [15] which remains the most commonly used to date. This method is a modification of the one-step approach, with all perovskite precursors deposited in a single step, during which an antisolvent is applied triggering the crystallization of the perovskite film. [16] Similarly, several variations of deposition of perovskite layers by thermal evaporation have also been demonstrated. These include the single-source evaporation, sequential evaporation and multiple source coevaporation (Figure 1). Single-source evaporation is possible either via combining the perovskite precursors into a single crucible [17] or by first preparing (e.g., via solution-processing) perovskite crystals that are ground into a powder for evaporation. [18] Sequential evaporation follows a similar approach to that of the two-step solution-processed deposition, with each precursor evaporated separately, following by a thermal or vapor annealing. [19] The most common approach, however, is based on the multisource evaporation, in which each precursor is loaded into a separate crucible and is coevaporated along with all other precursors to form the perovskite layer. Importantly, unlike solution-processed perovskite films, it is possible to form crystalline perovskite layers by thermal evaporation without annealing; [20] however, many studies still rely on annealing for improving the evaporated films' properties. [21,22] It is noteworthy that many additional methods for the deposition of perovskite films exist such as inkjet printing, [23] spray coating, [24] chemical vapor deposition, [25] flash evaporation, [26] and many others; [27] however, these methods are less common in literature and generally show lower performance than those fabricated by the methods outlined above. The last decade has seen remarkable advancements in the field of perovskite materials and photovoltaic technologies. One of their most extraordinary characteristics is the high quality of layer...

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“…The improved V bi can originate from the interfacial band alignment induced by MEA passivation with an interfacial dipole layer, which directs the dipole moment away from the TiO 2 surface. [ 22,32 ] Therefore, the incorporation of MEA between the m‐TiO 2 film and perovskite spontaneously improves V oc in the passivated device.…”

Section: Resultsmentioning

confidence: 99%

Efficient Bifacial Passivation Enables Printable Mesoscopic Perovskite Solar Cells with Improved Photovoltage and Fill Factor

et al. 2020

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Surface defects, which mediate nonradiative recombination, are detrimental to both the photovoltaic performance and stability of perovskite solar cells (PSCs). Improving photovoltage and fill factor (FF) in screen‐printed mesoporous PSCs is a major challenge for approaching the power conversion efficiency (PCE) of the planar configured devices. Herein, a novel bifacial passivation strategy which simultaneously suppresses deep trap states within TiO2 and perovskite through interaction between functional groups and defects is demonstrated for fully printable mesoscopic PSCs. The application of monoethanolamine (MEA) treatment to TiO2 surface not only reduces the energy barrier between TiO2 and perovskite for accelerating the charge transfer but also passivates the uncoordinated Pb defects on the perovskite interface. Due to the synergistic effect of charge extraction promotion and trap passivation, the fabricated PSCs deliver a champion PCE of 15.5% with an enhanced Voc of 0.94 V and FF of 70.4% compared with PSCs without MEA passivation, and the device maintains 97% of its topmost PCE after 240 h under constant simulated solar illumination in air atmosphere. This investigation helps exploit new approaches for defect passivation to further improve both the efficiency and stability of printable mesoscopic PSCs.

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Enhancing the Open-Circuit Voltage of Perovskite Solar Cells by Embedding Molecular Dipoles within Their Hole-Blocking Layer

Cited by 32 publications

References 59 publications

Facile Physical Modifications of Polymer Hole Transporting Layers for Efficient and Reproducible Perovskite Solar Cells with Fill Factor Exceeding 80%

Facile Physical Modifications of Polymer Hole Transporting Layers for Efficient and Reproducible Perovskite Solar Cells with Fill Factor Exceeding 80%

The Future of Perovskite Photovoltaics—Thermal Evaporation or Solution Processing?

Efficient Bifacial Passivation Enables Printable Mesoscopic Perovskite Solar Cells with Improved Photovoltage and Fill Factor

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