Interfacial Modification For The Fabrication Of Highly Efficient And Stable Perovskite Solar Cells

Perovskite solar cells(PSCs)have been rapidly emerging as one of the most promising candidates for the next generation of thin film photovoltaics within a mere few years.The current certified power conversion efficiency(PCE)of PSCs is over 20%,approaching the champion efficiency of the industry flagship material of silicon.However,the hysteresis issue and long-term stability are still limiting the practical application of PSC devices.The work of this thesis is mainly focus on the chemical analysis and interfacial modification for the fabrication of highly efficient and stable PSCs.This thesis will be divided into eight chapters,and the main results are as follows:Chapter 1.The basic concepts of the perovskite and the development process of the perovskite solar cell are presented.The main problems of the perovskite solar cell and the solutions reported in the literature are summarized.The purpose and significance of this paper are put forward.Chapter 2.An effective interfacial modification strategy employing thiols has been adopted to enhance the performance and stability of PSCs.Modification at the TiO2/perovskite interface by HOOC-Ph-SH facilitated the formation of larger perovskite crystallites,and improved the transfer of photo-generated electrons from perovskite to TiO2 as well.The enhanced cell performance was observed.Furthermore,modifying the interfaces of perovskite/hole transport layers using hydrophobic thiols,especially HS-PhFs,remarkably enhanced the cell stability in air or under AM 1.5 G solar light illumination.Chapter 3.A thiolated nanographene was employed as a new type of hole transporting material in perovskite solar cells to achieve efficient charge extraction from perovskite,yielding the perfect cell performance.The efficiency was readily improved by doping with graphene sheets into nanographene to improve the charge transfer.More importantly,beneficial from the hydrophobic nature of nanographene,the devices exhibited significantly improved device stability under AM 1.5G illumination in the humidity about 45%without encapsulation.Chapter 4.Two new types of organic molecules containing S,N atoms have been designed and synthesized,and used as hole transport materials to assemble PSCs.The final optimal PSC device achieved 13%in photoelectric conversion efficiency,and exhibits relatively high stability.In order to futher improve the cell performance and stability,thiourea was used to modify perovskite films.Such a modification produced a thin PbS layer in situ on the perovskite surface.The presence of PbS layer achieved the fabrication of efficient and stable PSC devices.Chapter 5.Surface-clean Pd nanosheets were synthesized and successfully used as an effective dopant of hole transport material to enhance the conductivity of the hole transport layer.Applying only a trace amount of Pd nanosheets readily led to a remarkably enhanced photon-to-current efficiency of PSCs.Such a similar strategy suggests the possibility to use surface-clean Pd nanosheets to enhance the performance of PSCs based on organic hole transport materials.Chapter 6.During the past two years,the introduction of DMSO has revolutionized the fabrication of high-quality pervoskite films for solar cell applications.By capturing and solving the molecular structures of several intermediates involved in the fabrication of perovskite films,we developed a new effective protocol to fabricate high-performance PSCs.The best efficiency of fabricated MAPbI3 PSCs was up to 19.0%.As compared to the previously reported DMSO method,the devices fabricated by the method reported in this work displayed high performance and reproducibility.Chapter 7.Although the power conversion efficiency of PSCs has been up to 22.1%in recent years,however,the hysteresis issue are still limiting the practical application of PSCs.It is well known that TiO2 has a relatively lower electron mobility,further causing the imperfect interfacial contact and severe charge recombination between the Ti02 and perovskite interface.The electron mobility of ZnO is several orders higher than that of TiO2,however,there is severe charge recombination at the interface of ZnO/perovskite diminishing the cell efficiency and stability.Here we modified the surface of ZnO layer with protonated ethanolamine bridged by MgO to construct a perfect interface contact.By using such an modification,the best efficiency was up to 21.1%with free hysteresis.The cell stability was also significantly enhanced.Furthermore,employing graphene with good hydrophobicity and thermal conductivity to encapsulate as-fabricated PSCs devices enabled the realization of stable PSCs devices.Chapter 8.Conclusion and perspective are given in this chapter.