Polymer Hole Transport Material Functional Group Tuning for Improved Perovskite Solar Cell Performance

Abstract

As lead halide perovskites (LHPs) continue to achieve success as a lightharvesting material in perovskite solar cells (PSCs), exploring and understanding other materials in the device stack become increasingly important. Particularly, selection of suitable hole transport materials (HTMs) that demonstrate high performance and stability is imperative in the design of P−I−N PSCs. Presented here are a family of 12 structurally related polymers based on either fluorene or carbazole main chains with select aromatic side groups that introduce tunable properties for use in PSCs. How properties such as the highest occupied molecular orbital energy level, conductivity, glass-transition temperature, and wettability of the HTM affect the PSC performance is explored. Devices that incorporate the polymer HTMs perform well relative to PTAA in benchmark P−I−N PSC architectures while exhibiting similar or superior stability under accelerated aging studies. The relative synthetic simplicity and resultant performance of the HTMs in PSCs coupled with the ability to customize properties with different functional groups demonstrates the potential of this family of HTMs for a variety of LHP materials.

Origins of Photoluminescence Instabilities at Halide Perovskite/Organic Hole Transport Layer Interfaces

“…Finally, this comprehensive picture provides deeper insight into our previous study on perovskite solar cell performance using a similar set of organic HTLs. 67 In particular, the opencircuit voltage (V OC ) of mixed iodide/bromide perovskite solar cells is observed to increase as the HTL HOMO level becomes deeper up to ∼−5.1 eV, which corresponds to a similar level where we observe HTL/iodine reactions to slow significantly but then plateaus for even deeper HOMO energies. Our results here demonstrate that non-radiative recombination is dominated by the iodine-doped HTL region for shallower HOMO levels, where interfacial non-radiative recombination limits V OC .…”

Thermal Properties of Polymer Hole-Transport Layers Influence the Efficiency Roll-off and Stability of Perovskite Light-Emitting Diodes

“…In view of this, we propose that it is important to further design and explore polymer HTLs with both high electrical conductivity and high T g for high-performance PeLED applications. 27,32 It should be said that PTAA, the most thermally stable polymer employed in this work, does not have a measurable T g and thus might be a good example of a thermally stable polymer as we demonstrate. As a general guidance for the future synthesis and study of other polymer charge-transport layers, it is in general a balance between solubility and T g .…”

“…On the other hand, the operational lifetime of PeLEDs is more closely related to the thermal stabilities of their polymer HTLs, and our work shows that PeLEDs using high glass transition temperature polymers can sustain more than 11.7 million electrical pulses at 1 kA cm –2 . In view of this, we propose that it is important to further design and explore polymer HTLs with both high electrical conductivity and high T g for high-performance PeLED applications. , It should be said that PTAA, the most thermally stable polymer employed in this work, does not have a measurable T g and thus might be a good example of a thermally stable polymer as we demonstrate. As a general guidance for the future synthesis and study of other polymer charge-transport layers, it is in general a balance between solubility and T g .…”

Polymer Boosts High Performance Perovskite Solar Cells: A Review

“…[149] By modifying the structure of the main chain, introducing blocks and functional groups, many polymer HTMs with excellent properties can be obtained. [150] Some polymers are used as undoped HTMs (such as PFBTI, TABT, and PBDB-Cz), and the PCE of their modified devices has exceeded that of PSCs based on traditional HTMs (such as Spiro-OMeTAD, PTAA, and PEDOT: PASS). [133,136,139] Polymer as HTMs can not only promote the efficient migration of holes from perovskite to HTL, but also effectively passivate the surface defects through the charged functional groups on the chain.…”