High Open Circuit Voltage for Perovskite Solar Cells with S,Si-Heteropentacene-Based Hole Conductors

Abstract

High photovoltage in perovskite solar cells (PSCs) can be achieved by designing new hole transporting materials (HTMs) with relatively deeper energy levels of the highest occupied molecular orbital (HOMO). Here, we report on the synthesis of a new heteroacene-based HTM (HTM-1) and demonstrate its potential in the fabrication of FAPbBr3 [FA = CH(NH2)2] PSCs yielding VOC as high as 1.55 V, a record value for this light harvester. The energetic position of the frontier orbitals of HTM-1 was estimated using electrochemical measurements, and the charge transport across the interfaces was studied using steady-state and time-resolved photoluminescence. When spiro-OMeTAD (HOMO = –5.1 eV) is replaced with HTM-1 (HOMO = –5.3 eV), the VOC increases from 1.51 to 1.55 V, whereas the JSC value decreases from 7.0 to 5.7 mA cm–2. The similar trade-off between JSC and VOC is observed for efficient iodide-based PSCs, suggesting that there is a critical energy level for the HOMO below which overall photovoltaic performance will suffer. After probing at a maximum power point under full-sun illumination at 60 °C for a duration of 120 h, the FAPbBr3 PSCs based on HTM-1 retained ≈ 95 % of their initial efficiency, which demonstrates their robust operational stability.