**4. Conclusions**

In this paper, the PEDOT-GO composite film was successfully prepared as a hole transport layer for the PSCs. The functional thin film significantly inhibited the recombination of holes and electrons, improved the current density, and finally enhanced the PCE of the PSCs. With the mass ratio of 0.75, the highest PCE reaches 14.09%, which is 26% higher than that of the HTL-free sample, and similar results were obtained from Spiro-OMeTAD devices. Compared with Spiro-OMeTAD, PTAA, P3HT, and other traditional hole transport materials, it is much cheaper and more suitable for large-scale applications.

**Author Contributions:** Conceptualization, J.L. and S.W.; Data curation, T.Y.; Formal analysis, T.Y.; Investigation, J.L. and T.Y.; Methodology, S.W.; Resources, T.Y. and S.W.; Writing—original draft, T.Y.; Writing—review & editing, J.L. and S.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** Key Program for Intergovernmental S&T Innovation Cooperation Projects of National Key R&D Program of China (No. 2019YFE0107100).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Xinfang Cui from the shiyanjia lab for the SEM analysis (www.Shiyanjia.com).

**Conflicts of Interest:** The authors declare no conflict of interest.
