Interface Engineering For High-performance Qrganic/Perovskite Solar Cells

Organic bulk heterojunction solar cells(OSCs)and hybrid halide perovskite solar cells(pero-SCs)are two promising photovoltaic techniques for the next-generation energy conversion devices.The rapid increase in the power conversion efficiency(PCE)in OSCs and pero-SCs has profited from synergetic progresses in rational material synthesis for photoactive layers,device structure optimization,and interface engineering.Interface properties in these two types of devices play a critical role in charge extraction,interfacial recombination,surface trap passivation,device stability,and sunlight utilization.Therefore,great efforts were devoted to controlling interface for improving the solar cell performance Thus,this thesis tends to explore transporting layer materials to enhance the ability of charge transport and extraction.Meanwhile,these materials were also used to passivate the defect at perovskite interface.In addition,we also fabricated the colorful semitransparent OSCs(ST-OSCs)by precisely controlling interface structure.The main results are as follows.1.We designed,synthesized a hydrophilic fullerene derivative[6,6]-phenyl-C61-butyric acid-(3,4,5-tris(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)phenyl)methanol ester(PCBB-OEG)and introduced as additive in the methylammonium iodide precursor solution in the preparation of MAPbI3 perovskite film by two-step sequential deposition method,and obtained a top-down gradient distribution with an ultrathin top layer of PCBB-OEG.Meanwhile,a high-quality perovskite film with high crystallinity,less trap-states,and dense-grained uniform morphology was also obtained.When the PCBB-OEG containing perovskite film(pero-0.1)is prepared in a p-i-n planar pero-SC with the configuration of ITO/PTAA/pero-0.1/PC61BM/Al,the device delivers a promising power conversion efficiency(PCE)of 20.2%without hysteresis.Importantly,the pero-0.1-based device shows an excellent stability.2.We used an ultrathin bulk-heterojunction(BHJ)organic semiconductor(PBDB-T:ITIC)layer as an intermediary between the hole transporting layer and Sn-Pb-based low-bandgap perovskite film to minimize Eloss.It is found that this BHJ PBDB-T:ITIC intermediary simultaneously provided a cascading energy alignment in the device,facilitated high-quality Sn-Pb perovskite film growth,and passivated the anti-site defects of the perovskite surface.In this simple way,the Eloss of the pero-SCs based on(FASnI3)0.6(MAPb I3)0.4(bandgap≈ 1.25 eV)is dramatically reduced below 0.4 eV,leading to a high open-circuit voltage(Voc)of 0.86 V.As a result,the best pero-SCs showed a significantly improved PCE of 18.03%with negligible J-V hysteresis and high stability.3.A crystallizable small molecule 4,4’-(4,8-bis(5-(trimethylsilyl)thiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline)(BDT-Si)was synthesized for using as a molecular additive to enhance the intermolecular stacking of PTAA film and reduce the disorder energy,leading to an improved mobility of PTAA film.The enhanced mobility of the HTM could promote the transport in the HTL at the interface and then hinder the surface recombination.In addition,BDT-Si could shift the Highest Occupied Molecular Orbital(HOMO)level downward,which further increase the hole extraction at surface between perovskite film and HTMs.As a result,the p-i-n planar pero-SCs with BDT-Si as an additive in PTAA HTL film show the best PCE of 21.67%.Importantly,the related device also shows good stability with retaining 86%of this initial efficiency after 1000 hours of storage in ambient atmosphere without encapsulation and 80%of its initial PCE under continuous illumination after 500 hours.4.We fabricated inverted ST-OSCs with high-quality hybrid Au/Ag transparent top electrodes and fine-tuned dielectric mirrors(DMs).It is demonstrated that the device color can be tailored and the light harvesting in the OSCs can be enhanced by matching the bandgap of the polymer donors in the active layer with the specifically designed maximum-reflection-center-wavelengths of the DMs.Furthermore,the inverted ST-OSCs based on PTB7-Th:PC71BM with six pairs of DMs demonstrate a PCE of 7.0%with an average visible transmittance(AVT)of 12.2%.The device design and processing method are also successfully adapted to a flexible substrate,resulting in a device with a competitive PCE of 6.4%with an AVT of 11.5%.