| With the decrease of fossil energy and the aggravation of environmental pollution,new energy,especially solar energy,has developed rapidly.Perovskite-’based solar cells have become a hot research topic in the third generation of new solar cells.Perovskite materials have the advantages of low exciton binding energy,high carrier mobility,long diffusion distance and wide optical absorption range,adjustable band gap,rich material storage,low production cost.Since 2009,the power conversion efficiency of perovskite solar cells(PSCs)has increased from 3.81%to 24.2%.The efficiency of PSCs is almost comparable to that of commercial monocrystalline silicon solar cells.It is generally believed that PSCs are the most promising commercial solar cells for the next generation.But before commercialization,there are still some problems to be solved,especially the stability of PSCs.In this paper,the self-assembly and in situ passivation of the electron transport layer(ETL)are used to form a good film morphology and interface,which can enhance the efficiency of PSCs.Meanwhile,it also improves their thermal and photo-stability.Specific research mainly includes the following two aspects:1.Perovskite solar cells are promising photovoltaic devices with high efficiency beyond 24%,but thermal instability is one of the key obstacles for the commercialization.To prolong thermal stability of PSCs,we doped(4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine(n-DMBI)into a state-of-the-art fullerene derivative(PTEG-1)with a hydrophilic triethylene glycol type side chain as ETL in planar PSCs with low-temperature process(＜100 ℃).The addition of dopant in PTEG-1 ETL results in stable self-assembly layered structure.We observe that the increase of ETL conductivity and reduction of work function facilitate charge extraction and improve the energy level alignment.As a result,CH3NH3PbI3-based n-i-p perovskite cells with doped ETL exhibit a hysteresis-free power conversion efficiency of 18.5%,outperforming the ones based on pristine ETL(16.2%)or the other fullerene derivatives.Strikingly,the corresponding unsealed devices show long-term thermal stability.Devices sustain 85%of their initial efficiency after 1000 h storage under 60 ℃ with the humidity of 20%.Our work bodes well for the dawn of commercialization of perovskite devices,providing the chance for the exploration of such high-efficiency devices with long-term thermal stability on flexible substrates.2.TiO2 is a common ETL for high-efficiency PSCs.However,the ultraviolet photocatalysis of TiO2 and existence of intrinsic oxygen vacancies easily result in perovskite film degradation,which lead to charge recombination at the interface between TiO2 and perovskite,thus affecting the long-term photo-stability for TiO2-based PSCs under full spectral continuous illumination.To solve the issues,here we study dopamine-capped TiO2 nanoparticles as ETL.Dopamine forms chelating effect with TiO2 via in situ passivation,and improves interface bonding between TiO2 and perovskite active layer.The introduction of dopamine can substantially reduce oxygen vacancies and suppress deep trap states within TiO2.In addition,the terminal amino groups in dopamine can passivate the uncoordinated Pb atoms and decrease the Pb-I/Br antisite defects at the interface of perovskite/TiO2.As an interfacial crosslinking agent,dopamine can not only reduce charge-accumulation and charge-recombination rate,but also increase charge-extraction efficiency at the TiO2 and perovskite interface.Based on the dopamine-capped TiO2 nanoparticles surface,the corresponding planner Cs0.05FA0.81MA0.14PbI2.55Br0.45 PSCs deliver a power conversion efficiency of nearly 21%with negligible hysteresis.Moreover,unencapsultated devices retain 80%of their initial performance after 1200 hours under illumination in nitrogen atmosphere.In general,this chemical-bath-deposited dopamine-modified TiO2 provides an effective commercialized route for efficient and photostable planar PSCs. |
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