Solution-processed TiO2 as a hole blocking layer in PEDOT:PSS/n-Si heterojunction solar cells Md. Enamul Karim, A.T.M. Saiful Islam, Yuki Nasuno, Abdul Kuddus, Ryo Ishikawa and Hajime Shirai EPJ Photovolt., 11 (2020) 7 Published online: 09 July 2020 DOI: 10.1051/epjpv/2020004