Extremely simple one-step coating ITO-free inverted polymer solar cells (IFIPSCs) have been fabricated
using a novel film deposition method—doctor blading technique, which is completely compatible with
roll-to-roll (R2R) manufacturing. Delamination of the interfacial buffer layer (IBL) from the photoactive
mixtures is achieved via a spontaneous vertical self-assembly. The performance of one-step doctorblading
IFIPSCs is primarily influenced by the inherent IBL stratification purity rather than the fine donor/
acceptor phase separation for the rigid backbone PTB7 system, which is significantly different from that
of the conventional two-step doctor blading devices. The surface energy results strongly demonstrate
that the formation of the interfacial layer between the ITO-free cathode and the photoactive layer is
significantly controlled by the solvent drying time, which determines the self-assembly quality and can
be greatly manipulated from 2700 to 1200 s by different substrate temperatures. It's worth noting that
the pure interfacial layer formed at low substrate temperatures improves charge separation and
transport, whereas high substrate temperatures limit its growth, leading to the decrease of device
performance. The detailed relationship between the self-assembly interfacial layer and the internal
resistance and capacitance is revealed by impedance spectroscopy. Encouraging power conversion
efficiency (PCE) of 6.56% is achieved from simple one-step doctor-blading ITO-free devices at a very
low substrate temperature of 25 C, which is energy saving and appropriate for industrialized R2R
production. In contrast, the highest PCE of 7.11% ever reported for two-step doctor-blading ITO-free
IFIPSCs was obtained at a high substrate temperature of 60 C for achieving a fine morphology without
regard to the vertical delamination. Furthermore, for crystalline polymer systems like P3TI with a semiflexible
chain, it requires a higher substrate temperature of 40 C to mediate the balance of vertical selfassembly
stratification of the interfacial buffer layer and photoactive morphology to maximize the device


Yuanbao Lin,Chaosheng Cai,Yangdong Zhang,Wenhao Zheng,Junyu Yang,Ergang Wangb and Lintao Hou.