Impact of work function of back contact of perovskite solar cells without hole transport material analyzed by device simulation

The impact of the work function of a metal back contact on lead methylammonium tri-iodide based perovskite solar cells without hole transport material (HTM) was analyzed using device simulation. The elimination of the HTM is attractive in terms of the simplification of device structure and fabrication process. In the solar cell, a back junction is formed by the perovskite absorber and metal back contact. The device simulation revealed that the elimination of the HTM did not change the built-in voltage (V_bi) of the device when the work function of the metal back contact (?_M) was similar to the valence band maximum of the absorber (E_{v_absorber}). In the HTM-free structure, V_bi showed a high value if ?_M was equal to or deeper than E_{v_absorber}. In contrast, when ?_M was shallower than E_{v_absorber}, V_bi monotonically decreased, resulting in the decrease in open-circuit voltage of the device. The results showed the importance of the ?_M matching to maintain V_bi, which is useful guideline for the design of the HTM-free perovskite solar cells.