Minimizing Open-Circuit voltage deficit via interface engineering for highly efficient CsPbI2Br perovskite solar cells

Abstract

• 1. Bilayer ETL ZnO/Mg x Zn 1-x O and HTL dopant-free PM6 are introduced. • 2. ZnO/Mg x Zn 1-x O provides a cascaded energy level alignment with CsPbI 2 Br. • 3. ZnO/Mg x Zn 1-x O improves CsPbI 2 Br film quality. • 4. PM6 energetically aligns better with CsPbI 2 Br than spiro-OMeTAD. • 5. CsPbI 2 Br-based PSCs delivers a champion PCE over 16% with V OC deficit of 0.58 V. All-inorganic perovskite CsPbI 2 Br is a promising wide bandgap light absorber for tandem solar cells owing to its appropriate bandgap and great thermal stability. However, high open-circuit voltage ( V OC ) deficit has been a major obstacle for obtaining high efficiency in CsPbI 2 Br-based solar cells and thus limiting their application. Herein, we employ a strategy of interface engineering that deploys a bilayer electron transporting layer (ETL) and dopant-free hole transporting layer (HTL) to significantly mitigate the energy loss. A bilayer ETL ZnO/Mg x Zn 1-x O and Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)] (PM6) are energetically more compatible with the energy band of CsPbI 2 Br than ZnO and 2,2′,7,7′-tetrakis (N, N-di-p-methoxy-phenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), which facilitate the photogenerated electron and hole transfer at perovskite/charge transporting layer interfaces. Moreover, the quality of the CsPbI 2 Br perovskite film deposited atop bilayer ETL ZnO/Mg x Zn 1-x O is substantially enhanced compared to that on top of ZnO. Both the more favorable energy level alignment and reduced defect density alleviate energy loss in the resultant solar cells. Perovskite solar cells with the structure of ITO/ZnO/Mg x Zn 1-x O/CsPbI 2 Br/PM6/MoO 3 /Ag give rise to an open-circuit voltage ( V OC ) of 1.34 V, which is one of the highest V OC among all-inorganic CsPbI 2 Br solar cells. The resultant V OC deficit drops to be lower than 0.6 V. As a result, the optimized all-inorganic CsPbI 2 Br-based solar cells yield a champion power conversion efficiency of 16.04%.