Preparation Of Highly Efficient And Stable Perovskite Solar Cells Based On Doped Nickel Oxide Hole-transporting Layer

Organic-inorganic hybrid perovskites have become one of the most attractive photoelectric materials due to their advantages,such as high absorption coefficient,high carrier mobility,long charge diffusion length,direct band gap and low exciton binding energy,and so on.The photoelectric conversion efficiency（PCE）of perovskite solar cells（PSCs）have increased rapidly from 3.8%to 23.7%within ten years.Among various PSC device structures,the inverted planar device has gained extensive attention due to its facial fabrication,simple device structure and low hysteresis.In inverted planar PSCs,hole transport materials（HTMs）play multiple roles,which not only extract/transport holes and block electrons effectively,but also have great impacts on the crystallinity and crystal growth of perovskite thin films,as well as the stability of PSCs.Many kinds of materials have been applied as HTMs in inverted planar PSCs,mainly including organic and inorganic p-type semiconductors.Compared with organic HTMs,inorganic HTMs are particularly attracting the interest of researchers because of their outstanding stability,higher carrier mobility,p-type semiconducting nature,low cost and easier processing via solution from precursors and nanoparticles.In particular,owing to the wide band gap,high optical transmittance,excellent energy level alignment with the perovskite absorbers and good chemical stability,NiO_x HTMs have been widely employed in inverted planar PSCs and the NiO_x-based PSCs have demonstrated very promising PCEs of over 20%along with higher fill factor（FF）and longer device lifetime.Despite these merits,the low intrinsic electrical conductivity of the pristine NiO_x has seriously hindered further improvement of NiO_x-based PSCs,which will result in the increased charge recombination and reduced hole extraction.To overcome this drawback,considerable efforts have been successfully put forth to increase the electric conductivity of NiO_x.Among these,one effective approach is doping.Firstly,a lithium and silver co-doping strategy has been successfully implied to prepare NiO_x films for high performance inverted planar PSCs.Compared to the pristine and single-doped NiO_x,the Li and Ag co-doping approach exhibits the synergistic effect and can endow NiO_x films with higher electrical conductivity,higher hole mobility and better interface energy band alignment with perovskite active layers.Moreover,the perovskite film with enhanced crystallinity can be obtained induced by the Li,Ag:NiO_x film.The PSC with Li,Ag:NiO_x HTM shows a high power conversion efficiency（PCE）up to 19.24%and less hysteresis effect,which outperforms the devices with the pristine NiO_x or single-doped NiO_x HTLs.Meanwhile,the Li,Ag:NiO_x device can retain 95%of its initial PCE after storage at the relative humidity of 30±2%in 30 days without encapsulation.Secondly,a carbon quantum dots（CQDs）hybrid strategy has been successfully implied to prepare NiO_x films for high performance inverted planar PSCs.Compared to the pristine NiO_x,the CQDs/NiO_x hybrid films exhibit higher electrical conductivity,higher hole mobility and better interface energy band alignment with perovskite active layers.Moreover,the perovskite film with enhanced crystallinity and good preferred orientation can be obtained induced by the 3wt%CQDs/NiO_x hybrid film.The PSC with 3wt%CQDs/NiO_x HTM shows a high power conversion efficiency（PCE）up to 19.20%with high open-circuit voltage(V_oc),less hysteresis effect and outstanding stability.Our work provides effective approaches for realizing efficient p-type NiO_x HTM and promising strategies for the preparation of highly efficient and stable NiO_x based inverted planar PSCs.