Interfacial Transport Materials Of Inverted-Structure Perovskite Solar Cells

Due to the excellent ambipolar charge transport ability,long carrier diffusion length,small exciton binding energy and high absorption coefficient in visible region of the organic-inorganic hybrid perovskite materials such as MAPbX3(X=I,Br,and Cl),organic-inorganic hybrid perovskite solar cells(PSCs)have received considerable attentions with the power conversion efficiency(PCE)increasing from an initial value of 3.8%to a certificated value of 23.7%in recent years.The typical device structures of PSCs mainly include three types ranging from mesoscopic to planar heterojunction structures with conventional-structure(n-i-p)or inverted-structure(p-i-n)layouts.Among them,inverted-structure PSCs have attracted a great deal of attention due to its low temperature fabrication process and suppressed current-voltage hysteresis.In the fields of perovskite solar cells,the mismatch of energy levels of perovskite layer and electrodes as well as the existence of numerous defect states on the surface of perovskite layer leads to the difficulty of extraction photogenerated carriers from perovskite layer,resulting in the inferior device efficiency and stability.Incorporating interfacial transport materials between the perovskite layer and electrodes is an effective strategy to impove the device performance.In this dissertation,we focused on developing new interfacial transport materials and modifying the existing interfacial transport materials by elemental doping,and carried out the following works:1.A non-conj ugated polymer poly(vinylpyrrolidone)(PVP)was inserted between the electron transporting layer PC61BM and cathode Ag,leading to enhanced device performance of inverted-structure planar heterojunction(PHJ-PSCs)from 10.83%to 12.55%.Among the photovoltaic parameters determing the device performance,fill factor(FF)exhibits an obvious increase from 58.98%to 66.13%.This is because the incorporation of PVP leads to the formation of a dipole layer which enhances the built-in potential across the device.Besides,the interfacial contact between PC61BM and Ag is improved resulting in a suppressed charge recombination.2.By doping the hole transport layer(HTL)nickel oxide(NiOx)with non-metallic element nitrogen,the PCE of the inverted-structure PHJ-PSC device reaches 17.02%,which increases by?11.4%relative to that of the control device(15.28%).Besides,the device stability test proves that the incorporation of nitrogen into NiOx can effectively improve the ambient stability of the device.The performance enchancement of PSCs is mainly attributed to the improved conductivity and crystallinity of NiOx film upon nitrogen doping.Furthermore,the valence band maximum of NiO.is lowered from-5.32 eV to a more negative value of-5.43 eV.As a result,the energy barrier between perovskite layer and HTL is effectively reduced.Besides,the crystallinity of the perovskite layer is improved with a reduced trap density.Therefore,the hole transporting efficiency within the device is enhanced leading to an improved device performance.3.Tin(IV)(SIn4+)was incorporated into nickel oxide(NiOx)film.Under the optimized Sn4+doping ratio(1 at%),the PCE of the inverted-structure PHJ-PSC device reaches 18.04%,which increases by?6.8%relative to that of the control device(16.89%).The PCE enhancement is mainly attributed to the increase of open circuit voltage(Voc)with a value of 1.06 V for the device with Sn4+doped NiO.as HTL in relative to that of the control device(1.02V)with pristine NiO.as HTL.The incorporation of Sn4+ into NiO.effectively improves the conductivity of NiOx and increases the work function of NiOx leading to an enhanced built-in potential across the device which consequently reduces interfacial charge accumulation and facilitates charge transport in the interface.As a result,the hole transporting efficiency within the device is enhanced leading to an improved device performance.