The electron transport layer in perovskite solar cell (PSC) is composed of electron transport materials (ETM). The perovskite light-absorbing layer forms electron-selective contact with the ETM, and the ETM extracts and transfers photogenerated electrons from the perovskite layer, which can effectively block the movement of holes toward the cathode and prevent the recombination of electrons and holes from affecting the device performance. The dynamic processes of charge extraction, transfer, and charge recombination at the perovskite/electron transport layer interface directly affect the performance of PSC. In order to further improve the photoelectric conversion efficiency and stability of PSC, the ETM should meet the following requirements: 1) the energy level is suitable, that is, the lowest unoccupied molecular orbital (LUMO) of the ETM is aligned with the conduction band of the perovskite light absorption layer; its highest occupied molecular orbital (HOMO) is matched with the valence band of the perovskite light absorption layer , which is conducive to the cooperative transport of carriers and reduces the probability of carrier recombination; 2) high electron mobility and conductivity, the rapid extraction and transfer of electrons by ETM is beneficial to reduce the power loss of the device and suppress the polarization-exciton annihilation, thereby improving the photoelectric conversion efficiency of the device; 3) high transparency, especially when light is incident into the device, the electron transport layer should avoid competing absorption with the perovskite absorber layer; 4) good thermal and chemical stability and solution processability, enabling the formation of dense continuous pinhole-free high-quality films when preparing electron transport layers. As the core component of PSC, ETM has a huge impact on the efficiency, cost and stability of PSC.
Figure 1. Chemical structures of some organic electron transport materials