Gradient Engineered Light Absorption Layer for Enhanced Carrier Separation Efficiency in Perovskite Solar Cells

Abstract

Carrier transport behavior in the perovskite light absorption layer significantly impacts the performance of perovskite solar cells (PSCs). In this work, reduced carrier recombination losses were achieved by the design of a band structure in perovskite materials. An ultrathin (PbI 2 /PbBr 2) n film with a gradient thickness ratio was deposited as the lead halide precursor layer by a thermal evaporation method, and PSCs with a gradient band structure in the perovskite absorption layer were fabricated by a two-step method in ambient atmosphere. For comparison, PSCs with homogeneous perovskite materials of MAPbI 3 and MAPbI x Br 3 − x were fabricated as well. It is found that the gradient type-II band structure greatly reduces the carrier lifetime and enhances the carrier separation efficiency. As a result, the PSCs with a gradient band structure exhibit an average power conversion efficiency of 17.5%, which is 1-2% higher than that of traditional PSCs. This work provides a novel method for developing high-efficiency PSCs.

Constructing an Interfacial Gradient Heterostructure Enables Efficient CsPbI3 Perovskite Solar Cells and Printed Minimodules

“…It can be verified that, the Br − or Cl − ion concentration gradually decreases from the upper to the bottom of the perovskite films, and the BTA + content at the film bottom is almost negligible, that is, the bottom of CsPbI 3 ‐BTABr or CsPbI 3 ‐BTACl film can be considered to be pristine CsPbI 3 . [ 10b,26 ] Therefore, Figure S19 (Supporting Information) can depict the variations of energy levels of perovskite films based on BTABr and BTACl, where Fermi levels balance at the same level due to the electron and hole flow in the opposite direction. And the difference between the E f and E V in the upper part is smaller than that in the bottom part, which is beneficial for charge separation.…”