Extending the Absorption Spectra and Enhancing the Charge Extraction by the Organic Bulk Heterojunction for CsPbBr3 Perovskite Solar Cells

Among the various lead halide perovskites, inorganic cesium lead bromide (CsPbBr3) was considered as a promising candidate for new solar cells because of its unique photophysical properties and outstanding stabilities in a high-humidity, high temperature, or ambient atmosphere. However, the efficiency is still quite limited due to the inefficient charge transfer and narrow spectra. In this work, we report that integrating the P3HT/PCBM bulk heterojunction (BHJ) organic layer with the CsPbBr3 films can sharply enhance the spectral absorption from 540 to 680 nm and simultaneously enhance the charge extraction ability at the CsPbBr3/carbon interface. At the same time, the carbonyl group and thiophene units in the BHJ group can inhibit the production of Pb-0 defects and passivate the under-coordinated Pb2+, thus reducing trap density, retarding charge recombination, and improving charge transport and extraction. Using this strategy, the efficiency of BHJ/CsPbBr3 solar cells is improved from 5.36 to 8.15%. In addition, the integrated devices have superior long-term stability, and unpackaged devices can maintain an initial efficiency of 90% within 40 days. This work provides an avenue for the industrial application of this integrated device in the future.