Strong electron acceptor additive based spiro-OMeTAD for high-performance and hysteresis-less planar perovskite solar cells

Abstract

As the most popular hole-transporting material (HTM), spiro-OMeTAD has been extensively applied in perovskite solar cells (PSCs). Unluckily, the pristine spiro-OMeTAD film has inferior conductivity and hole mobility, thus limiting its potential for application in high-performance PSCs. To ameliorate the electrical characteristics of spiro-OMeTAD, we employ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a strong electron acceptor into spiro-OMeTAD in PSCs. The incorporation of DDQ with spiro-OMeTAD not only improves the conductivity and the Fermi energy level, but also reduces the trap states and nonradiative recombination, which accounts for the remarkable enhancement in both the fill factor (FF) and open-circuit voltage (V _OC) of PSCs. Consequently, the champion PSC with DDQ doped hole transport layer (HTL) generates a boosted power conversion efficiency (PCE) of 21.16% with an FF of 0.796 and a V _OC of 1.16 V. Remarkably, DDQ modified devices exhibit superb device stability, as well as mitigated hysteresis. This study provides a facile and viable strategy for dopant engineering of HTL to realize highly efficient PSCs.

Fig. 1. (a) Photos of DDQ (middle), pure spiro-OMeTAD (left) and a mixture of them (right) in solid state. (b) Photos of D-spiro-OMeTAD (right) and U-spiro-OMeTAD (left) in chlorobenzene solution. (c) UV-vis absorption spectra of P-spiro-OMeTAD, U-spiro-OMeTAD and D-spiro-OMeTAD. (d) Schematic illustration of the architecture of PSC.

Fig. 2. (a) SEM of cross-sectional image of the corresponding device with D-spiro-OMeTAD film. (b) J–V characteristics of devices with HTLs doped by various concentration of DDQ. (c) J–V characteristics of PSCs using spiro-OMeTAD with and W/O DDQ, measured at both forward and reverse scanning directions. (d) The steady-state J_SC and PCE output of the optimal PSC using DDQ doped HTL.

Fig. 3. The statistical data based on 30 independent control and DDQ doped devices: (a) V_OC, (b) J_SC, (c) FF and (d) PCE.

Fig. 4. UPS of the spiro-OMeTAD films with or W/O DDQ incorporation: (a) E_onset region, (b) E_cutoff region. (c) Tauc plots of the HTLs with or W/O DDQ. (d) Energy levels of the perovskite and various HTLs.

Fig. 5. (a) PL spectra and (b) TRPL spectra of pristine perovskite and perovskite/spiro-OMeTAD with different dopants. (c) Tafel plots of devices based on HTLs with and W/O DDQ. (d) Dark J–V curves of hole-only devices based on spiro-OMeTAD HTL with and W/O DDQ.

Fig. 6. (a) V_OC values of the PSCs using the HTLs with or W/O DDQ as a function of light intensity. (b) Nyquist plots of the PSCs doped with or W/O DDQ obtained in the dark condition. (c) Stability test for the efficiencies of the unpackaged devices based on doped or undoped spiro-OMeTAD HTLs.