Monitoring Thermal Annealing of Perovskite Solar Cells with In Situ Photoluminescence

Abstract

organic cations. This unprecedented fast development stimulates further research in this unique class of solutionprocessable semiconducting materials. Next to improving device performance, examples of current issues in the field are the fabrication of tandem devices, [6,7] concerns about lead toxicity, [8,9] device stability, [10] the photophysical properties, [11,12] and upscaling of the fabrication protocols. [13,14] By now many different processing routes have shown to lead to highly efficient methylammonium lead triiodide (MAPbI 3 ) solar cells. For example, various lead sources have been used in a single-step routine, such as lead acetate (Pb(OAc) 2 ), lead chloride (PbCl 2 ), and lead iodide (PbI 2 ), [15] or combinations thereof. [16,17] Other recipes that yield efficiencies exceeding 13% use different solvents, [18] nonsolvent washing, [19,20] alkyl halide additives, [21] acid additives, [22,23] hot casting, [23,24] and multistep processing routes. [3,25,26] The development of such a multitude of procedures is, at least in part, a consequence of the fact that it is not straightforward to reproduce the highest efficiency cells among different research groups. Whether this relates to differences in material sources and equipment, or to a lack of experience, is presently unknown. However, it evidences that there is generally a narrow processing window for high-efficiency perovskite solar cells.A clear example of the subtleties in the processing of perovskite layers is the sensitivity to the exact thermal annealing conditions, such as duration and temperature, [27][28][29] which have resulted in the development of complex, e.g., ramped, annealing schemes. [30][31][32] The optimal annealing conditions may change with choice of precursors, deposition conditions, substrate type, and layer thickness. Thus, it is desirable to monitor annealing in situ, to find the optimal annealing time during the process itself, rather than after completing the entire solar cell. Two characterization methods are typically used to monitor the formation of a perovskite film during annealing: optical absorption [33,34] and X-ray diffraction (XRD). [33,35,36] However, changes in the absorption spectrum can be subtle, and are not easily related to device performance (see ref. [29] and this work). XRD is a powerful tool to study the formation of crystal structures, but is difficult to implement in situ in standard fabrication. Most importantly, the disadvantage of both methods is that they Layer deposition of organometal halide perovskites for solar cells usually involves tedious experimentation to establish the optimum processing conditions. Important parameters are the time and temperature of thermal annealing. Here, it is demonstrated that in situ photoluminescence allows to determine the optimal annealing procedure without fabricating complete solar cells. A deposition method is used in which dense layers of perovskite crystals are formed within seconds in ambient air by hot casting a mixture of lead acetate, lead chloride, and me...

A Biopolymer Heparin Sodium Interlayer Anchoring TiO2 and MAPbI3 Enhances Trap Passivation and Device Stability in Perovskite Solar Cells

“…As an affirmation of the XPS results, we performed DFT calculations to examine the surface adsorption properties. For simplicity, we divided the polymeric HS into two repeat units A and B with the four different binding groups (see Figure a, denoted as A1: COO − , A2: OSO 3 − ; B1: CH 2 OSO 3 − , B2: NHSO 3 − ) and concerned all the possible adsorption structures on the (110) surfaces of MAPbI 3 and TiO 2 films which were chosen based on the XRD results (see Figure a,b). Specifically, units A and B tend to bind with single Pb atom ( d OPb of ≈2.4 Å) at the MAPbI 3 surface and to the two adjacent titanium atoms ( d OTi of ≈2.0 Å) at the TiO 2 surface.…”

Inkjet‐Printed Micrometer‐Thick Perovskite Solar Cells with Large Columnar Grains

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Coated and Printed Perovskites for Photovoltaic Applications

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