Poly(ethylene glycol) diacrylate (PEGDA) is introduced into the SnO 2 dispersion as the polymer framework to hinder the agglomeration. The PEGDA-modified SnO 2 acted as the electron transport layer (ETL) in n-i-p structured perovskite solar cells (pero-SCs). It is demonstrated that the PEGDA plays multifunctional roles in the enhancement of photovoltaic performance and stability against illumination and humility. First, the PEGDA-modified SnO 2 ETL is more uniform, and its energy level matched well with the perovskite, which could facilitate the carrier transport and reduce the energy loss. Second, PEGDA could passivate the defects at the interface between perovskite and ETL. Eventually, a power conversion efficiency (PCE) of 23.31% is achieved for the α-FAPbI 3 based pero-SCs. Most importantly, the unencapsulated devices maintained more than 90% of the initial PCE after 850 h continuous illumination (100 mW/cm 2 ). This study could provide insight for the low-cost, facile, and efficient interface modification for the pero-SCs.

The average values and the deviations are calculated from 20 independent devices; b) The current density calculated from the EQE spectra.

Poor stability of spiro-OMeTAD hole transport materials (HTMs) with dopant is a major obstacle for the commercialization of perovskite solar cells (pero-SCs). Herein, we demonstrate a series of quinoxaline-based D-A copolymers PBQ5, PBQ6 and PBQ10 as the dopant-free polymer HTMs for high performance pero-SCs. The D-A copolymers are composed of fluorothienyl benzodithiophene (BDTT) as D-unit, difluoroquinoxaline (DFQ) with different side chains as A-unit, and thiophene as π-bridge, where the side chains on the DFQ unit are bi-alkyl for PBQ5, bi-alkyl-fluorothienyl for PBQ6, and alkoxyl for PBQ10. All the three copolymers are adopted as the dopant-free HTM in the pero-SCs. The planar n-i-p structured pero-SCs based on (FAPbI 3 ) 0.98 (MAPbBr 3 ) 0.02 with PBQ6 HTM demonstrated the high power conversion efficiency (PCE) of 22.6% with V oc of 1.13 V and FF of 80.8%, which is benefitted from the suitable energy level and high hole mobility of PBQ6. The PCE of 22.6% is the highest efficiency reported in the n-i-p structured pero-SCs based on dopant-free D-A copolymer HTM. In addition, the pero-SCs show significantly enhanced ambient, thermal and light-soaking stability compared with the devices with traditional spiro-OMeTAD HTM.

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