HTL-Free Perovskite Solar Cells with a Carbon Electrode and Enhanced Stability, Through a Scalable Polymer Treatment Method

Perovskite solar cells with a carbon electrode (C-PSCs) are considered the most promising and viable structure for the upscaling and future commercialization of PSCs. With the ability to be fabricated with industrially compatible methods and with no need for employing hole transport materials, C-PSCs are not randomly moving to the forefront of PSC research at the moment. In this work, hole transport material (HTM)-free C-PSCs have been fabricated under entirely ambient conditions. The devices employ an additive-free, methylammonium-free perovskite, which has been deposited with the infiltration method, with no antisolvent extraction method employed. The solar cells prepared exhibit photocurrent values as high as 26.28 mA/cm 2 , open circuit voltage values as high as 907 mV, fill factor values as high as 0.52, and power conversion efficiency (PCE) up to 12%. With the scope of delivering devices with enhanced lifetime, post-treating the C-PSCs with two different polymers, namely poly methyl methacrylate and poly vinyl pyrrolidone, has been proposed and their efficacy has been evaluated. By using a simple and scalable method, and after optimization of the post-treatment conditions, C-PSCs that retain > 80% of their initial PCE after more than 30 days of storage under uncontrolled ambient conditions (ISOS-D1 protocol) and with no additional encapsulation method employed, have been achieved. The results have been confirmed by x-ray diffraction (XRD) measurements, contact angle measurements, while scanning electron microscopy (SEM) images shed light on the impact of ambient atmosphere overtime in the polymer layers that have been formed, confirming the superiority of poly(methyl methacrylate) as a porotective layer. This result can contribute to the stability issues that PSCs face, during both their fabrication in ambient conditions and their respective devices’ lifetime, and push the technology one step further towards their commercialization.