Enhanced crystallization of solution-processed perovskite using urea as an additive for large-grain MAPbI3perovskite solar cells.

Perovskite crystal quality plays an important role in perovskite solar cells, given that multiple grain boundaries and trap states in the perovskite films hamper further enhancement of solar cell efficiency. Using the solution method to prepare perovskite films with large grains and high coverage requires further improvements. Herein, we introduce Lewis base urea as an additive into the precursor of perovskite to control the crystallization dynamics, allowing for large-grain crystal growth. As a result, MAPbI3films with urea as an additive are well crystallized with large crystal grains of sizes >3µm. The large-grain perovskite is found to simultaneously improve the power-conversion efficiency (PCE) and device stability. With an optimal urea additive of 20 mol%, the PCE is significantly increased from 15.47% for the reference MAPbI3solar cell to 18.53% for the device with MAPbI3with urea as an additive. Finally, the optimized device demonstrates excellent stability and maintains 80% of the initial PCE after 60 days.

A sandwich-like electron transport layer to assist highly efficient planar perovskite solar cells.

Co-modification of an electron transport layer (ETL) with metal oxides and organic molecules can optimize the structure of the ETL and improve the performance of perovskite solar cells (PSCs). Here, a sandwich-structured ETL consisting of MgO/SnO2/EA was designed by co-modifying a SnO2 ETL with magnesium oxide (MgO) and ethanolamine (EA). The device with an ETL modified with MgO and EA has excellent performance in enhancing electron transport and blocking holes. It also inhibits the formation of deep defect states and improves the stability of the device. The introduction of MgO effectively improves the open-circuit voltage (VOC) of the device, while EA increases the short-circuit current density (JSC). The optimal efficiency of the PSC using the ETL co-modified with MgO and EA is 20.23%, which is much higher than that of the device with the unmodified SnO2 ETL (17.94%). The method described here provides an effective way to develop high performance ETLs co-modified with metal oxides and organic compounds for perovskite-based optoelectronic devices.