Enhanced Performance Of Perovskite Solar Cells Using Surface And Interface Regulation

Organic-inorganic hybrid perovskite draws a lot of attention in photovoltaic industry due to their excellent properties such as high light absorption coefficient,relative low photo-generation excition bingding energy,higher carrier mobility and long carrier diffusion lengths,ambipolar charge transport ability,solution processability and low cost raw materials.Today,the power convension efficiency（PCE）of perovskite solar cells（PSCs）hired the organic-inorganic hybrid perovskite as light active layer is over 22%,showing an attractive application prospect.However,there are still some urgent challenges for commercialization of PSCs,especially to improve the PCE and stability.In this work,we take the mesoscopic PSCs as research object,regularized the surface and interface of devices,optimized the device structure,improved the carrier transport abilities,enhanced the perovskite film quality and reduced the defects at the surface and interface.The PCE and stability of PSCs was much improved using these strategies,and we got some interesting results.The main research contents and results are as follows:1.A type of quasi-mesoscopic PSCs（QM-PSCs）with circular disk like porous hierarchical TiO₂（hier-TiO₂）nanostructures of scattered distribution as scaffold layer was developed.The porous hier-TiO₂ nanostructures were synthesized by burning off the orgainic components of MIL-125（Ti）metal-organic frameworks（MOFs）,which were scatteredly distributed on compact TiO₂ layer to form quasi-mesoscopic hier-TiO₂ scaffold.The quasi-mesoscopic hier-TiO₂ scaffold can provide large spaces for the full infiltration of perovskite precursor to achieve excellent contact between perovksite and TiO₂ electron transport layer and grow large grain sizes perovskite.The quasi-mesoscopic hier-TiO₂scaffold effectively solved the problem that perovskite precursor can not fully infiltrate into TiO₂ layer to generate pore defects at the interfaces which is caused by the traditional mesoscopic TiO₂ scaffold consisting of small TiO₂ nanoparticles（npt-TiO₂,²0 nm）with the labyrinthine structure and narrow space.Besides,the strong light scattering ability of hier-TiO₂ scaffold layer can improve the incident light use ratio,which was benefical to improving the current density of solar cells.As a result,the QM-PSCs show a best PCE of 16.56%,much higher than that（11.38%）of M-PSCs with conventional mesoscopic npt-TiO₂ scaffold.In addition,the high quality perovskite film on hier-TiO₂ scaffold layer improved the device stability.The unencapsulated QM-PSCs can keep 47%of initial PCE afte aged for 30 days in 25℃,RH.³0%environment,however,the M-PSCs can only maintain 36%of initial PCE in same conditions.2.Because the hier-TiO₂ scaffold layer enhances the film quality of perovskite and provide good contact between perovksite and TiO₂,QM-PSCs show the superior photovoltaic performance and stability.Howerver,the inferior electron mobility of pure TiO₂ usually limits the transportation of photo-generated electrons.Furthermore,the defects of TiO₂ would trap the photogenerated carriers and increase carrier recombination.To solve this problem,the hier-TiO₂ scaffold layer was doped with lithium（Li）and the formed Li-hier-TiO₂ nanostructures show the same morphology with hier-TiO₂,but the trap states are much reduced and the electron transport abilities are improved.PSCs based on Li-hier-TiO₂ quasi-scaffold layer produce substantially higher PCE of 18.25%with suppressed hysteretic behavior.3.The surface morphology and crystallization quality of perovskite film was improved by incorporating terephthalic acid（TPA）into the perovskite precursor solution.The presence of TPA changed the crystallization kinetics of perovskite and formed some sheet-shaped perovskite near the crystal boundaries,which sutured the bottom grains into a grains-interconnected perovskite film.The interconnected grains are helpful to improve the carrier transportation and reduce recombination at grain boundaries.As a result,PSCs with TPA additive show a PCE of 18.50%,much higher than that（15.53%）of the pristine PSCs.The sutured grain boundries can resist the moisture or oxygen,which can restrain the corrosion of perovskite film through the grain boundries.The strong coordination between Pb²⁺and hydrogen bonds of hydroxyl groups in TPA can suppress the ion migration of perovskite and make it robust.The unencapsulated PSCs with TPA additive can keep 60%of initial PCE afte aged for 30 days in 25℃,RH.³0%environment,however,the pure PSCs can only keep 34%of initial PCE after 30 days in same conditions.Noticeably,the PSCs with TPA additive show the excellent thermal stability,which can keep 79%of initial PCE after 10 h baking under 100℃,and maintain 20%of initial PCE after 50 h baking under 100℃.However,the PCE of pure PSCs quickly reduces to22%of initial PCE in 10 h 100℃baking.4.Poly（9-vinylcarbazole）（PVK）was incorporated into the perovskite precursor solution to passivate the surface defects of perovskite films.The presence of PVK can also slow down the nucleation rate and grow large grain sizes perovskite film.The PVK passivated perovskite film with less surface defect density reduces the carrier recombination.PSCs based on PVK passivated perovskite film show a PCE of 16.78%with suppressed J-V hysteresis,much higher than that（15.53%）of the pristine PSCs.PVK passivation effects also enhanced the stability of PSCs.The unencapsulated PSCs passivated by PVK can keep 58%of initial PCE afte aged for 30 days in 25℃,RH.³0%environment,while the pure PSCs can only maintain 34%of initial PCE in same conditions.