Recently, all-polymer solar cells, in which both the donor and acceptor materials that absorb light and transport charges are semiconducting polymers, have a great potential to replace fullerene/polymer devices. The use of n-type polymers as acceptors has potential to overcome the high cost, poor thermal/photochemical stability, limited light absorption in the visible-near infrared region, and other limitations of fullerene derivatives. Among the various n-type polymers investigated as electron acceptors in all-PSCs to date, nanphthalene diimide (NDI)-based polymers with high carrier mobility and electron affinity have emerged as the most promising. Compared to fullerene derivatives, NDI-based n-type polymer acceptors exhibit better thermo/mechanical properties, light absorption and durability of the devices. The optical properties, electronic structure, crystallinity, solubility and charge transport of these materials can be easily tuned to enhance the devices performance. The greater thermal stability and mechanical strength of n-type polymers can ensure more morphologically and environmentally rugged all-polymer solar cells. In the paper, the research progress about the NDI-based D-A polymer acceptors is typically summed up according to the polymer structure. Meanwhile, the effects of corresponding donors, devices structure and post-process condition on the performances are described in detail. Finally, the all-polymer solar cells composed of NDI-based polymer acceptor and polymer donor are commented and we look forward to their development prospects in All-PSCs field.

Contents
1 Introduction
2 D-A polymers based on NDI
2.1 D-A polymers based on NDI which D unit has changed
2.2 D-A polymers based on NDI which A unit has changed
3 The devices post-processing technique
3.1 Solvent effect
3.2 The effect of D/A blend ratio on the device performance
3.3 The effect of additive on active layer morphology and device photovoltaic property
3.4 Film self-assembly aging
3.5 Invert structure of polymer solar cells
3.6 The cathode buffer layer
4 Conclusion and outlook