A counter electrode modified with renewable carbonized biomass for an all-inorganic CsPbBr3 perovskite solar cell

The cost associated with hole-transporting materials (HTMs) and electrodes made of noble metals is a recurrent problem for the widespread application of perovskite solar cells (PSCs). Biomass-derived carbons are green materials that have been incorporated in the electrodes of diverse electrochemical devices to reduce cost, improve environmental sustainability, and augment the specific surface area (SSA). Here, carbonized bacterial cellulose (CBC) and carbonized macadamia nutshell (CMNS) were combined with commercial carbon paste (CP) to fabricate counter electrodes (CEs) integrated into highly-stable all-inorganic CsPbBr3 PSCs synthesized by thermal evaporation. When electrically-conductive CP was mixed with either 0.1% CBC or CMNS, the power conversion efficiency was improved to 4.76% and 6.18%, respectively, compared to 4.45% for a PSC equipped with pure CP. The better performance of CMNS versus CBC in the CEs can be explained by a larger SSA, a more suitable work function, and a lower sheet resistance. The outstanding surface area of CMNS is likely to improve hole scavenging efficiency in the PSCs by increasing the number of contacts with CsPbBr3. The long-term stability of the all-inorganic CsPbBr3 PSC at high temperature was also improved with the CP CE modified with CMNS. These results demonstrate that adding CBC or CMNS to CP for the fabrication of CEs in a suitable ratio improves the photoelectric properties of all-inorganic PSCs and thus opens possibilities for novel applications for renewable and earth-abundant biomass-derived carbons.