Easy strategy to enhance thermal stability of planar PSCs by perovskite defect passivation and low-temperature carbon-based electrode

Organic-inorganic lead halide perovskite recently emerged as an efficient absorber material for solution process photovoltaic (PV) technology, with certified efficiency exceeding 25%. The development of low-temperature (LT) processing is a challenging topic for decreasing the energy payback time of perovskite solar cell (PSC) technology. In this context, LT planar n-i-p architecture meets all the requirements in terms of efficiency, scalability and processability. However, the long-term stability of LT planar PSC under heat and moisture stress conditions has not been carefully assessed. Here, a detailed study on thermal and moisture stability of large area (1 cm2) LT planar PSCs is presented. In particular, the key role on thermal stability of potassium iodide (KI) insertion in the perovskite composition is demonstrated. It is found that defect passivation of triple-cation perovskite by KI doping inhibits the halide migration induced from thermal stress at 85°C and delays the formation of degradation sub-products. The T80, defined as the time when the cell retains 80% of initial efficiency, is evaluated both for reference undoped devices and KI doped ones. The results show that T80 increases three times when KI doping is used. Moreover, an HTL free architecture where Au top electrode is replaced with low-T screen-printable carbon-paste is proposed. The combination of carbon-based HTL free architecture and KI-doped perovskite permits to increase the T80 from 40h to 414h in unsealed devices.