Study On Interfacial Control In Efficient And Stable Perovskite Solar Cells

Perovskite solar cells(PVSCs)have aroused much attention with several desired properties for photovoltaic applications,including large absorption,high mobility,long carrier-diffusion lengths,facile tunable bandgaps and various processing methods.At present,the certified power conversion efficiency of PVSCs has been improved to 25.2%.However,many obstacles limit the commercialization of perovskite devices,such as the uncontrollable perovskite film quality,the poor stability of the device and toxicity of lead.The morphology of perovskite films is essential to fabricate the high efficiency and stable PVSCs.Unsatisfactory,significant defects are inevitable during the preparation of perovskite films,which reduce the performance of perovskite devices.In addition,the hole transporting layer(HTL)plays an important role in improving charge extraction,reducing interfacial recombination and modifying band alignment etc.The low conductivity of the hole transport layer nickel oxide affects the perovskite device performance in the p-i-n perovskite structure.Therefore,it is very important to reduce the perovskite film defects,optimize the whole device structure for achieving the efficient and stable perovskite devices.In this paper,we mainly focus on the modification of the perovskite layer and the hole transport layer.The improving the quality of perovskite films can reduce defects in perovskites,promote carrier transmission and reduce carrier recombination in order to improve the photoelectric performance of perovskite devices.In addition,tin-based PVSCs are used instead of traditional lead-based perovskites to avoid the use of toxic lead.Besides,doping improves the conductivity of the hole transport layer nickel oxide,enhances hole extraction and reduces recombination losses to obtain a highly efficient and stable perovskite device.The paper mainly includes the following parts:(1)It is critical to achieve the high-quality perovskite film morphology and delicate interfacial modification for realizing high performance PVSCs.Molybdenum isopropoxide(Mo-IPA)was applied to optimize perovskite film morphology and interface of perovskite layer during perovskite film fabrication process with two-step method.Both highly crystalline perovskite film and MoOx interfacial layer were simultaneously achieved after treated with Mo-IPA instead of IPA.Compared to pure IPA treatment,the Mo-IPA treatment could induce a denser and more uniform morphology of perovskite film with larger crystals size.At the same time,the formation of MoOx by annealing of Mo-IPA can effectively elevate the valence band maximum of perovskite layer,resulting to favor a better energy alignment with 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene(Spiro-MeOTAD)for efficient hole extraction.These advantages significantly increased the photovoltaic performance of the PVSCs from 10.8%to 12.0%.(2)The HTL plays an important role in achieving high efficient and stable p-i-n inverted PVSCs by improving charge extraction,reducing interfacial recombination and modifying band alignment etc.Rubidium doped nickel oxide(Rb:NiOx)was employed as the HTL to improve the optoelectronic properties and the photovoltaic performance of PVSCs.The Rb:NiOx films exhibited better conductivity and effectively elevated the valence band maximum with a simple solution-based method.Meanwhile,the Rb doping induced a better morphology of perovskite film with larger crystals size on top.Therefore,Rb doping resulted in significantly improved hole extraction and reduced recombination.As a result,the photovoltaic performance of the PVSCs was remarkably increased from 14.48%to 17.21%.(3)Fullerene end-capped polyethylene glycol(C60-PEG)was introduced to improve the perovskite films morphology and the device stability.C60-PEG could enlarge the perovskite crystals size and passivate the defects of perovskite films,facilitating the carrier transport and hindering the carrier recombination.Consequently,the superior optoelectronic properties were attained with an improved power conversion efficiency of 17.71%for the perovskite device with C60-PEG treatment.Meanwhile,amphiphilic C60-PEG enhanced the resistance of perovskite films to moisture.After 40 days,the C60-PEG based devices without encapsulation remained 93%and 86%of the original power conversion efficiency under nitrogen and ambient condition(25? temperature,60%humidity),respectively.(4)It is challenging to simultaneously fabricate high-performance and stable Sn-based perovskite device owing to the inferior Sn-based perovskite film and the fast oxidation of Sn2+to Sn4+.Herein,a simple approach was employed by adding an additive of aminoguanidine hydrochloride(NH2GACl)in perovskite precursor solution.The higher film quality was obtained due to the formation of strong hydrogen bonding between halide ions in the perovskite and NH2GACl,which helps to passivate the defects and lessen Sn2+oxidation.In addition,NH2GACl addition can effectively adjust the energy level alignment between Sn-based perovskite and adjacent layer to facilitate the charge transportation.The perovskite device modified with NH2GACl achieved a power conversion efficiency up to 7.3%,retaining 90%of its initial efficiency after 30 days in a nitrogen glovebox.