Sequential Coating of Perovskite Layers via Sub-Stoichiometric Precursors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in forming large-scale, defect-free perovskite solar cells lies in the difficulty of achieving a continuous, uniform photoactive layer due to rapid crystallization and issues like dewetting and pinhole formation in scalable coating processes, which are exacerbated by the volatile nature of ammonium halides used in conventional sequential deposition methods.
Innovation Solution
A process involving a sequential coating method where a first precursor solution with a non-stoichiometric amount of ammonium halide (AX) is applied to a substrate, followed by a second precursor solution to form a perovskite layer (AMX3), with the molar ratio of MX2:AX set between 1:n with 0 < n < 1, allowing for controlled crystallization and incorporation of AX into the final layer without contaminating the composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sequential deposition methods are used with stoichiometric ammonium halide, then complete perovskite conversion is achieved, but rapid crystallization causes dewetting, pinholes, and non-uniform film formation
Solution Approach 1:
The patent applies partial action by using a sub-stoichiometric amount of ammonium halide (AX) in the first precursor solution (molar ratio MX2:AX = 1:n where 0 < n < 1). This deliberate deficiency prevents rapid crystallization and dewetting while the subsequent second precursor solution provides the remaining AX needed for complete perovskite conversion, thus resolving the contradiction between conversion completeness and film uniformity.
2Manufacturing precision
If spin coating is used to form uniform perovskite films, then homogeneous crystal structure is achieved over large areas, but the process cannot be scaled up for industrial production
Solution Approach 1:
The patent changes the crystallization kinetics parameter by controlling the AX concentration in the precursor solution (using sub-stoichiometric amounts). This parameter modification allows the perovskite formation to proceed slowly and uniformly during natural drying in scalable coating processes like slot-die coating, achieving film homogeneity without requiring spin coating, thus resolving the scalability contradiction.
3Productivity
If industrial scalable coating processes are used, then production speed is increased, but dewetting and pinhole formation occur due to different solution dynamics and drying times
Solution Approach 1:
The patent applies preliminary action by pre-forming a uniform MX2 intermediate layer with controlled morphology through sub-stoichiometric AX addition before the final perovskite conversion. This intermediate layer serves as a template that prevents dewetting and pinhole formation during the subsequent conversion step, enabling scalable coating processes to produce defect-free films while maintaining high production speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the yield and efficiency of perovskite solar cells by acting as a kinetic barrier in crystallization, forming a uniform crystal structure and enhancing the production speed of perovskite solar cells, while maintaining the integrity of the perovskite composition.
Implementation Method 1
The first precursor solution is applied to a substrate to form a first precursor coating, the first precursor coating is dried to form a solid MX2 coating layer
Implementation Method 2
a conversion process to AMX3. In the present invention, a coating of AX is applied to the first coating which reacts with MX2 to convert MX2 to AMX3. The AX from the first precursor solution is incorporated into the final perovskite layer AMX3. When the process is scaled up, a continuous film layer comprising a uniform crystal structure is difficult to fabricate due to this rapid crystallisation.
Data Source
Figure 1A~2(B)
Figure 3
Figure 4~5
AI summary
A process of forming a photoactive layer of a planar perovskite photoactive device comprising: applying at least one layer of a first precursor solution to a substrate to form a first precursor coating on at least one surface of the substrate, the first precursor solution comprising MX2 and AX dissolved in a first coating solvent, wherein the molar ratio of MX2:AX = 1:n with 0 < n < 1; and applying a second precursor solution to the first precursor coating to convert the first precursor coating to a perovskite layer AMX3, the second precursor solution comprising AX dissolved in a second coating solvent, the first precursor solution reacting with the second precursor solution to form a perovskite layer AMX3 on the substrate, wherein A comprises an ammonium group or other nitrogen containing organic cation, M is selected from Pb, Sn, Ge, Ca, Sr, Cd, Cu, Ni, Mn, Co, Zn, Fe, Mg, Ba, Si, Ti, Bi, or In, X is selected from at least one of F, Cl, Br or I.