Improvement in polymer solar cell performance and eliminating light soaking effect via UV-light treatment on conjugated polyelectrolyte interlayer

•Efficient inverted polymer solar cells using PFBD as electron transporting layer were fabricated.•Light soaking issue was eliminated by pre-UV treatment.•Pre-UV treatment on PFBD leads to reduced work function and increased electron mobility.•The performance of UV-treated PFBD based solar cell was stable for at least 26 days.

A new conjugated polyelectrolyte material, namely, poly [9,9-bis((6′-N,N,N-trimethylamino)hexyl)-fluorene-alt-co-benzoxadiazole dibromide] (PFBD) is reported as electron transport layer (ETL) in polymer solar cells. We observed a light-soaking effect and described how a pre-UV light treatment on PFBD ETL is essential for attaining higher efficiencies (>7%) and negate the light-soaking problem. The pre-UV light treatment on PFBD layer is found to directly influence its molecular structure and result in reduction of the work function and increased electron mobility in PFBD which corroborates well with the observed lower series resistances obtained from dark current analysis and impedance spectra, and therefore enhancement in open-circuit voltage and fill factor. Moreover, after the pre-UV light treatment, the maximal efficiency of the solar cells retains at a nearly similar level for at least 26 days.

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