Light-induced improvement of dopant-free PTAA on performance of inverted perovskite solar cells

Poly (triaryl amine) (PTAA) is one of the promising hole transport materials (HTM) for perovskite solar cells. Highly efficient PTAA-devices have been demonstrated in both direct (n-i-p) and inverted (p-i-n) architectures. In the inverted structures, the device suffers from poor coverage of the perovskite film over the hydrophobic PTAA surface. To address this issue, we exploited an easy and efficient approach utilizing a short-time UV treatment of the PTAA layer prior to the perovskite deposition. The UV-treatment improved the optical properties of PTAA layers, which synergistically helps the light harvesting of the perovskite. Enhanced grain sizes, together with the decrease of recombination centers in the UV treated dopant-free PTAA, lead to efficient perovskite solar cell with PCE reaching 19.17% for 0.09 cm2 active area. Moreover, the device retains over 75% of its initial efficiency after 1400 h storage in ambient condition with average relative humidity (RH) of 50%. Additionally, the effect of UV light was studied on PTAA with different molecular weights. Non-destructive UV exposure more predominantly improved the efficiency of lower molecular weight PTAA-based device. A maximum PCE of 12.3% for 1 cm2-sized cells using 5 min-UV PTAA with low MW is achieved. This investigation points to the main roles of the HTL quality for the development of high-efficiency photovoltaic solar cells and provides a fast, easy and cost-effective method toward upscaling.