Close-Space Sublimation as a Scalable Method for Perovskite Solar Cells

Vacuum techniques
for perovskite photovoltaics (PV) are promising
for their scalability but are rarely studied with techniques readily
adaptable for industry. In this work, we study the use of close-space
sublimation (CSS) for making perovskite solar cells, a technique that
has seen widespread use in industry, including in PV, and benefits
from high material-transfer and low working pressures. A pressed pellet
of formamidinium iodide (FAI) can be used multiple times as an organic
source, without needing replacement. Using CSS at a rough vacuum (10
mbar), efficient cesium formamidinium lead iodide perovskite based
solar cells are obtained reaching a maximum photoconversion efficiency
(PCE) of 18.7%. They maintain their performance for >650 h when
thermally
stressed at 85 °C in a nitrogen environment. To explain the initial
rise in PCE upon heating, we used drift-diffusion simulations and
identified a reduction in bulk trap density as the primary factor.