Perovskite solar modules have been attracting increasing attention due to their market potential, yet publications concerned with theintrinsic scale-up potential of different perovskite compositions remain relatively scarce. On the other hand, while great success is being made towards improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs) by cesium cation (Cs+) doping of the perovskite, more attention is being paid to the perovskite phase stabilization effect of Cs+ doping, and less to other properties that are critical to understand and futher improve the PSC's. In this work, moderately-Cs-doped MAPbI(3) was employed as a model perovskite material in order to exclude the phase stabilization effect. Our systematic study revealed the influence of Cs+ in organic-inorganic hybrid perovskites on the crystal structure, crystallization process, trap state density, band structure and charge (i.e., ions or photo-carriers) transport. Markedly, it has been observed that Cs+ doping can greatly increase the carrier diffusion length in the perovskite films, thus improving the potential to scale-up PSC's.The PCE of small area devices (0.09 cm(2)) was increased to 21.72% from 19.73%, with decreased hysteresis behavior and increased operational stability (T-85 = 1000 h) after Cs+ doped, where T-85 refers to the retention of 85% of the initial PCE. Moreover, a PCE of 21.08% was obtained for a Cs+-containing perovskite module with an active area > 30 cm(2), which demonstrates a better "reproducibility " than the reference sample (MAPbI(3)-based perovskite modules, PCE = 18.26%).