Role of in-situ substrate heating on the growth of perovskite films in printed perovskite solar cells

Detailed investigation has been performed for the effect of in-situ substrate heating on the growth of printed perovskite films towards getting high performance perovskite solar cells (PSCs). Perovskite layers and charge transport layers were printed by slot die method. The perovskite layers were printed in two steps, where first lead iodide (PbI₂) films were printed and then methyl ammonium iodide (MAI) ink was printed on them to convert PbI₂ into methyl ammonium lead iodide (MAPbI₃) perovskite. For the controlled growth of PbI₂ crystals the printed PbI₂ films were in-situ heated at different temperatures like 50^oC, 70^oC and 90^oC that resulted in formation of compact films with different crystal growths and phases, which affected the growth of perovskite crystals thereafter. It was difficult to convert the compact PbI₂ films completely into MAPbI₃ by one time printing of MAI, therefore the idea of multiple print cycles of MAI was implemented. The optimized print cycles of MAI led to achieve complete conversion of PbI₂ into high quality MAPbI₃ crystals, which resulted in PSCs having champion power conversion efficiency (PCE) up to 11.99%. The steady state PCE of the optimized cell did not exhibit any decay for > 200 s. Under continuous 1 sun illumination of a tungsten-halogen lamp, the optimized cells retained over 50% of their initial efficiency for up to ∼ 300 h. Subsequently, the solar modules printed with optimum print conditions in 9 cm × 13 cm area with an active area of 64.8 cm², exhibited PCE of 7.77%.