Publication date: 4th October 2024
All-inorganic CsPbBr3 perovskite solar cells (PSCs) have recently drawn significant attention due to their superior thermal stability. However, fabricating high-quality CsPbBr3 films through conventional one-step solution processing is quite challenging because of the poor solubility of CsBr in polar solvents. To overcome this limitation, we developed a Thiourea (T) -assisted one-step spin deposition method to enhance the crystallinity, phase purity, and grain size of CsPbBr3 films. By incorporating different amounts of Thiourea (T-10/T-20/T-30/T-40/T-50 mg/mL) into the precursor solution, T-30 led to a remarkable enhancement in power conversion efficiency (PCE), increasing it from 3.25% to 5.18%, representing a 59.4% improvement. This improvement is attributed to enhanced crystallinity and the reduction of trap states in the perovskite layer.
The optimized device architecture (FTO/c-TiO2/m-TiO2/CsPbBr3/Spiro/Au) with T-30 showed a JSC of 10.77 mA/cm2, a VOC of 0.70 V, and a fill factor (FF) of 0.68. XRD analysis revealed pronounced diffraction peaks at 15.6°, 22.08°, and 31.15°, corresponding to the CsPbBr3 phase, with the high intense peaks for the T-30 film, particularly at the (100) and (200) lattice orientations. Scanning electron microscopy (SEM) images demonstrated that Thiourea facilitates the formation of larger perovskite grains, resulting in compact films with minimal defects and smooth surfaces. UV-visible spectroscopy showed that the T-30 film exhibited the highest absorbance and a bandgap (Eg) of 2.3 eV. Photoluminescence (PL) measurements also indicated increased peak intensity, confirming reduced recombination. FTIR analysis revealed a shift in the C=S stretching vibration from 738 cm-1 to 745 cm-1, indicating strong interactions between Thiourea and PbBr2. The quantum efficiency (QE) spectra further supported the enhanced photocurrent response in the T-30 device. Importantly, the unencapsulated device maintained over 90% of its initial efficiency after 15 days under ambient conditions. This Thiourea-assisted strategy presents a promising route for fabricating stable, high-performance inorganic PSCs.
The authors express sincere gratitude to the Indian Nanoelectronics Users Programme-Idea to Innovation at IIT Madras (INUP-i2i, IITM), funded by the Ministry of Electronics and Information Technology (MeitY), for granting them access to device fabrication facilities at the Centre for NEMS and Nanophotonics (CNNP), IIT Madras. The authors would also like to thank Gujarat Council on Science and Technology (GUJCOST) sanction number GUJCOST/STI/2023-24/255 for providing financial support for the current research.The authors thank the Department of Science and Technology (DST), Government of India, for providing infrastructure assistance under the FIST grant, sanction number SR/FST/PS-I/2017/12.