As theory suggest...shift may be due to instrumental error, or stress nd strain in crystal....here you may be synthesizing it with same route...but control on crystal growth process is difficult...nd one of the common influencing factor is temperature...check for it.

Hybrid perovskites like CH3NH3PbI3 has a basic problem: stability or durability. There is abundant literature that reports degradation of this kind of samples. So, the XRD peaks could shift.

You may look for more reliable synthetic routes and go for papers, where the authors have confidently claimed long durability of synthesized samples.

Dopant plays a significant role in the XRD shift. This shift is may be positive or negative depends upon the size of the dopant atom and host atom. This shift occurs due to enlarged or reduced in interplanar spacings after the inclusion of dopant atoms.

See the following papers

https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/chem.202004902?af=R

Dear N. Rajamanickam this is certainly a very interesting technical question for many RG members working in the field of lead-based perovskites. For example, please have a look at the following relevant article in which the influence of temperature and crystal reorientation on the XRD pattern of methylammonium lead iodide perovskite is discussed in detail:

Crystal reorientation in methylammonium lead iodide perovskite thin film with thermal annealing

https://www.osti.gov/pages/servlets/purl/1515550

The paper has been published Open Access and can be freely downloaded as pdf file.

Apparently lattice strain can also have an influence:

Strained hybrid perovskite thin films and their impact on the intrinsic stability of perovskite solar cells

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1257&context=mechengfacpub

Moreover, as already mentioned by Sunil Barma small amounts of dopants can also have a significant influence. For more information about this effect please go though the following useful article:

Enhanced Grain Size and Crystallinity in CH3NH3PbI3 Perovskite Films by Metal Additives to the Single-Step Solution Fabrication Process

Article Enhanced Grain Size and Crystallinity in CH3NH3PbI3 Perovski...

This paper is freely available as public full text on RG.

Good luck with your research and best wishes! 👍

I thank Prof Frank T. Edelmann, Sunil Barma, Souvik Bhattacharjee, and Jignesh G. Hirpara for you detailed and valuable information's.

Dear Questioner, Kindly add the nearer ionic radius of the dopant atom. this is very helpful to unchanged the peak position. Also, properly analyzed the optimum temperature.