Solution processed pristine PDPP3T polymer as hole transport layer for efficient perovskite solar cells with slower degradation

We report solution processed pristine diketopyrrolopyrrole (DPP) based polymer (PDPP3T) as hole transport layer (HTL) for perovskite (CH₃NH₃PbI₃) solar cells. The pristine PDPP3T based perovskite solar cells achieved comparable photovoltaic performance (12.32%) as that (12.34%) of doped spiro-OMeTAD based cells. After exposing to air having 40% relative humidity at room temperature, PDPP3T based perovskite solar cells showed much slower degradation than spiro-OMeTAD cells. The PDPP3T based devices showed an efficiency decrease by 26.6% after being in air for 73 h and 60.6% for 172 h, while the spiro-OMeTAD cells exhibited a much larger efficiency decrease of 41.4% for 73 h and 82.9% for 172 h. The use of pristine PDPP3T does not require processing HTL in air and adding any additives such as lithium salt dissolved in acetonitrile, 4-tert-butylpyridine (TBP), which are needed for the spiro-OMeTAD HTL preparation. This prevents exposure of the perovskite layer to ambient air and avoids corrosion of perovskite layer by acetonitrile solvent and formation of PbI₂.xTBP complex which leads to slow down the cell degradation and improves device stability.