Tailoring organic bulk-heterojunction for charge extraction and spectral absorption in CsPbBr3 perovskite solar cells

Abstract

All-inorganic CsPbBr3 perovskite solar cells (PSCs) are promising candidates to balance the stability and efficiency issues of organic-inorganic hybrid devices. However, the large energy barrier for charge transfer and narrow spectral response are still two challenging problems for performance improvement. We present here an organic bulk-heterojunction {poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT: PCBM)} photoactive layer to boost the charge extraction and to widen the spectral absorption, achieving an enhanced power conversion efficiency up to 8.94% by optimizing the thickness of P3HT: PCBM photoactive layer, which is much higher than 6.28% for the pristine CsPbBr3 device. The interaction between the carbonyl group in PCBM and unsaturated Pb atom in the perovskite surface can effectively passivate the defects and reduce charge recombination. Furthermore, the coupling effect between PCBM and P3HT widens the spectral response from 540 to 650 nm for an increased short-circuit current density. More importantly, the devices are relatively stable over 75 days upon persistent attack by 70% relative humidity in air condition. These advantages of high efficiency, excellent long-term stability, cost-effectiveness and scalability may promote the commercialization of inorganic PSCs.