Charge selective contacts and interfaces for perovskite solar cells with improved stability and efficiency

Schutt, K

Abstract:: This thesis improves charge selective contacts for perovskite solar cells. First, mesoporous modification of n-type metal oxides is discovered to shift the work function of the perovskite, which enables n-type doping at the interface. A chapter on ZnO contacts elucidates chemical degradation mechanisms at the perovskite-ZnO interface, and a methylammonium-free perovskite is employed to suppress these reactions. Next, a Cs salt-treatment is developed to improve both the thermal stability and the Voc of cells on SnO2. In the following chapter, a novel organic p-type is one of the first alternatives to Spiro-OMeTAD that enables 20% power conversion efficiency. Finally, a dopant-free photo-cross-linkable polymer is presented that offers exceptional thermal stability for p-i-n cells, with device lifetimes exceeding 3,000 hours at 85°C.

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APA Style

Schutt, K. (2019). Charge selective contacts and interfaces for perovskite solar cells with improved stability and efficiency [PhD thesis]. University of Oxford.

MLA Style

Schutt, K. Charge Selective Contacts and Interfaces for Perovskite Solar Cells with Improved Stability and Efficiency. University of Oxford, 2019.

Chicago Style

Schutt, K. 2019. “Charge Selective Contacts and Interfaces for Perovskite Solar Cells with Improved Stability and Efficiency.” PhD thesis, University of Oxford.
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Authors

+ Schutt, K More by this author

Division:: MPLS
Department:: Physics
Sub department:: Condensed Matter Physics
Role:: Author

Contributors

+ Snaith, H

Role:: Supervisor

+ Marshall Aid Commemoration Commission More from this funder

DOI:: 10.5287/ora-v0nvzykox
Type of award:: DPhil
Level of award:: Doctoral
Awarding institution:: University of Oxford

Language:: English
Keywords:: Thin film

Photovoltaic
Subjects:: Perovskite solar cells

Charge selective contacts

Thin film solar
UUID:: uuid:4971f2a7-cc20-40a9-9e02-347ca47f438e
Deposit date:: 2020-03-06

Related item:: Overcoming Zinc Oxide Interface Instability with a Methylammonium‐Free Perovskite for High‐Performance Solar Cells
Description:: Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO2 and TiO2. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI3, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI3 interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO2‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO2, with many foreseeable advantages, provided that MA cations are avoided.
Related item:: Meso-superstructured perovskite solar cells: Revealing the role of the mesoporous layer
Description:: While perovskite solar cells (PSCs) have been developed with different device architectures, mesoporous devices have provided the highest power conversion efficiencies. In this work, the working mechanism of both positive-intrinsic-negative (p-i-n) and negative-intrinsic-positive (n-i-p) meso-superstructured (MSSC) PSCs, which include a thin interlayer of porous alumina at the bottom electrode, is explored. Interestingly, for both p-i-n and n-i-p architecture, the mesoporous configuration was more efficient than its planar counterpart. For MSSC SnO2-based n-i-p devices, that result was primarily due to an increase in Voc and Jsc, resulting from improved band alignment and filling of the electron trap states (n-doping at the SnO2/perovskite interface), which led to devices with 21.0% efficiency and 20.3% stabilized power output (SPO). Although MSSC NiOx-based p-i-n meso-superstructured devices were less efficient due to lower Voc, a slightly higher Jsc and fill factor improvement was achieved by the Al2O3 mesoporous layer, resulting in devices with 16.9% efficiency. Importantly, the electronic nature of the perovskite is dependent upon its physical confinement within a mesoporous scaffold. Therefore, either p- or n-type semiconductor/perovskite interfaces can be engineered by selectively modifying the semiconductor behavior with the introduction of an insulating mesoporous scaffold interlayer.
Related item:: A photo-crosslinkable bis-triarylamine side-chain polymer as a hole-transport material for stable perovskite solar cells
Description:: A crosslinkable acrylate random copolymer with both hole-transporting bis(triarylamine) and photocrosslinkable cinnamate side chains is compared to the widely used poly(4-butyl-triphenylamine-4′,4′′-diyl) (PolyTPD) as a hole-transport material (HTM) in positive–intrinsic–negative (p–i–n) perovskite solar cells (PSCs). The crosslinked films of this HTM exhibit improved wettability by precursor solutions of the perovskite relative to PolyTPD; this facilitates high-quality full film coverage by the subsequently deposited perovskite layer on smooth substrates, which is difficult to achieve with PolyTPD without the use of additional interlayers. PSCs fabricated using undoped and crosslinked copolymer achieve steady-state power outputs that are comparable to those of cells incorporating p-doped PolyTPD (with interlayers) as the HTM. The devices made with this material also exhibited improved initial stability under high-intensity ultraviolet LED irradiation, in comparison to those with the PolyTPD analogue. Remarkably, after 3000 h of aging in an oven at 85 °C in a nitrogen-filled glovebox, device efficiency showed no degradation; the SPO was comparable to the initial performance.
Related item:: New Generation Hole Transporting Materials for Perovskite Solar Cells: Amide‐Based Small‐Molecules with Nonconjugated Backbones
Description:: State‐of‐the‐art perovskite‐based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro‐OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT‐Amide‐TPA) is reported in which a functional amide‐based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g−1. When employed in perovskite solar cells, EDOT‐Amide‐TPA demonstrates stabilized power conversion efficiencies up to 20.0% and reproducibly outperforms Spiro‐OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT‐Amide‐TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li‐additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide‐based HTM can outperform state‐of‐the‐art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low‐cost HTMs.

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Copyright holder:: Schutt, K

Licence:: CC Attribution (CC BY)

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Charge selective contacts and interfaces for perovskite solar cells with improved stability and efficiency

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