Carbon Quantum Dots/TiO_x Electron Transport Layer Boosts Efficiency of Planar Heterojunction Perovskite Solar Cells to 19%

Abstract

In planar n-i-p heterojunction perovskite solar cells, the electron transport layer (ETL) plays important roles in charge extraction and determine the morphology of the perovskite film. Here, we report a solution-processed carbon quantum dots (CQDs)/TiO composite that has negligible absorption in the visible spectral range, a very attractive feature for perovskite solar cells. Using this novel CQDs/TiO ETL in conjunction with a planar n-i-p heterojunction, we achieved an unprecedented efficiency of ∼19% under standard illumination test conditions. It was found that a CQDs/TiO combination increases both the open circuit voltage and short-circuits current density as compared to using TiO alone. Various advanced spectroscopic characterizations including ultrafast spectroscopy, ultraviolet photoelectron spectroscopy, and electronic impedance spectroscopy elucidate that the CQDs increases the electronic coupling between the CHNHPbICl and TiO ETL interface as well as energy levers that contribute to electron extraction.

Band Alignment Engineering Towards High Efficiency Carbon‐Based Inorganic Planar CsPbIBr2 Perovskite Solar Cells

“…[22,34,35,[41][42][43] On the other hand, the narrower CBM differencei sg reatlyb eneficial to reduce interface recombination of chargec arriers, without loss in photo-current collection. The smaller work functiono fT iO 2 /CsBr suggests the possibility of ah igher builtin electric field in the resulting cell.…”

“…[23,[34][35][36] In general,i nterface recombination in PSCs depends not only on interfaciald efects, but also more importantly on the interfacial bands tructure, [37,38] which is both theoretically supported and experimentally demonstrated. [23,[34][35][36] In general,i nterface recombination in PSCs depends not only on interfaciald efects, but also more importantly on the interfacial bands tructure, [37,38] which is both theoretically supported and experimentally demonstrated.…”

Polymer Doping for High‐Efficiency Perovskite Solar Cells with Improved Moisture Stability

“…By measuring the intensity of S 2p (the characteristic peak for the J71), the distribution of polymer can be calculated. [47,48] However, neither XPS nor UPS shows any significant change following the J71 doping at different concentration ranging from 0.001 to 0.1%, indicating that the effective passivation layer on the perovskite surface uses too small amount of polymer for the XPS and UPS to pick it up. The energy level diagram is deduced from the optical bandgap, coupled with the Fermi level (E F ) and the valence band edge (E V ) derived from UPS.…”

A Rutile TiO2 Electron Transport Layer for the Enhancement of Charge Collection for Efficient Perovskite Solar Cells

“…And the decay kinetics of the band edge bleaching at the wavelength of 756 nm were checked (Figure 3c). [25,26] It is obvious that the peak intensity for the negative PB peak at about 756 nm is decreased for RT-ETL sample comparing with AT-ETL sample,i mplying that RT-ETL contributes to the exciton transition and charge extraction process from the MAPbI 3 film. Theformer is related to the exciton transition of MAPbI 3 film, while the later can be attributed to the absorption of transient species.…”