Perovskite solar cells (PSCs) have been demonstrated to be one of the most promising technologies in the field of renewable energy. However, the presence of the defects in the perovskite films greatly limits the efficiency and the stability of the PSCs. The additive engineering is one of the most effective approaches to overcome this problem. Most of the successful additives are extracted from the petroleum-based materials, while the research on the biomass-based additives is still lagging behind. In this paper, two ecofriendly hydroxyalkyl cellulose additives, i.e., hydroxyethyl cellulose (HEC) and hydroxylpropyl cellulose (HPC), are investigated on the performance of the MAPbI₃-based inverted PSCs. Due to the strong interaction between the hydroxyl groups of the cellulose and the divalent cations of the perovskite, these additives enhance the crystal grain orientation and significantly repair the defects of the perovskite films. Working as the additives, these two cellulose derivatives show a strong passivation ability, which significantly reduces the trap density and improves the optoelectronic feature of the PSCs. Compared with the average power conversion efficiency (PCE) of the control device (19.19%), an enhancement of ~10% is achieved after the addition of HEC. The optimized device (PCE = 21.25%) with a long-term stability (10:80 h, PCE = 20.93%) is achieved by the incorporation of the HEC additives into the precursor solution. It is the best performance among the PSCs with the cellulose additives up to now. This research provides a novel choice to develop a cost-effective and renewable additive for the PSCs with high efficiency and excellent long-term stability.

Green, biodegradable, and eco-friendly interface materials based on cellulose and its derivatives were prepared for organic solar cells (OSCs). In this work, calcium and two derivatives of cellulose with different carboxy acid groups, denoted as Cellulose-COOH and Cellulose-(COOH)_n, were used as cathode interfacial layers of OSCs, and a blend of the low-band-gap semiconducting polymers thieno[3, 4-b]thiophene/benzodithiophene (PTB7) and [6, 6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) was chosen as the photoactive layer. OSCs were fabricated with a configuration of indium-doped tin oxide (ITO) /poly(3, 4-ethylenedioxythiophene) : polystyrene sulfonate (PEDOT: PSS) /PTB7:PC₇₁BM/Ca or Cellulose-COOH or Cellulose-(COOH)_n/Al. As a result, the effect of cellulose-COOH was the best one among them, and the power conversion efficiency (PCE) reached 8.21% for the devices with cathode interfacial layer of Cellulose-COOH, which was better than that of OSCs using calcium as a modifier (PCE=7.95%). The favorable performance is attributed to the reduced work function and improved electron transfer caused by the introduction of carboxy cellulose between the active layer and the electrode. The developed technology shows great potential in accelerating the diversified applications of cellulose and producing cost-effective and eco-friendly interfaces for OSCs.