Quantitative phase analysis on Cs- and Rb-doped FAPbI3 and corresponding solar cell efficiency simulations

Abstract Stability and efficiency are two key indicators to evaluate the development prospect of perovskite materials in solar cells (SCs). The partial substitution of Cs or Rb for Formamidinium cation (FA) is proven to significantly improve the stability of FAPbI3. Phase compositions of Cs- and Rb-doped FAPbI3 play a crucial role in determining the stability, which still lack a deep understanding. Besides, bandgap variations upon adding Cs or Rb content also affect the SC efficiency, awaiting a detailed discussion. This work quantitatively analyzed the phase compositions of CsxFA1−xPbI3 and RbyFA1−yPbI3. Moreover, efficiencies of the CsxFA1−xPbI3 and RbyFA1−yPbI3 SCs were simulated using experimental data. The synchrotron X-ray diffraction patterns reveal that the Cs0.2FA0.8PbI3 sample contains the largest amount of the perovskite phase with Pm-3m symmetry, the non-perovskite phase with P63mc symmetry of FAPbI3 is effectively suppressed and therefore the structural stability is significantly improved. However, efficiency of the Cs0.2FA0.8PbI3 SC is slightly lower than that of the Cs0.15FA0.85PbI3 SC, ascribed to its enlarged bandgap and consequent narrowed light absorption waveband. For the RbyFA1−yPbI3 samples, the Rb0.05FA0.95PbI3 sample shows the best structural stability, and the corresponding SC achieves the highest efficiency.