A major limit for planar perovskite solar cells is the trap‐mediated hysteresis and instability, due to the defective metal oxide interface with the perovskite layer. Passivation engineering with fullerenes has been identified as an effective approach to modify this interface. The rational design of fullerene molecules with exceptional electrical properties and versatile chemical moieties for targeted defect passivation is therefore highly demanded. In this work, novel fulleropyrrolidine (NMBF‐X, XH or Cl) monomers and dimers are synthesized and incorporated between metal oxides (i.e. TiO2, SnO2) and perovskites (i.e. MAPbI3 and (FAPbI3)x(MAPbBr3)1‐x). The fullerene dimers provide superior stability and efficiency improvements compared to the corresponding monomers, with chlorinated fullerene dimers being most effective at coordinating with both metal oxides and perovskite via the chlorine terminals. The non‐encapsulated planar device delivers a maximum power conversion efficiency of 22.3% without any hysteresis, while maintaining over 98% of initial efficiency after ambient storage for 1000 h, and exhibiting an order of magnitude improvement of the T80 lifetime.

Charge transport layers (CTLs) are critical for achieving high power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, the p-type bulk heterojunction (p-BHJ, i.e., PCBM doped PTAA) and n-type BHJ (n-BHJ, i.e., PBDTTT-C-T doped PCBM) charge transfer complexes are employed as hole and electron transport layers, respectively, to fabricate inverted PSCs. The photo-induced charge transfer between p-type and n-type organic semiconductors in the BHJ layers provides extra photoconductivity for enhanced charge transport and quasi-Fermi level splitting, hence enhancing the fill factor and open-circuit voltage of PSCs. The p-BHJ layer helps to improve the crystallinity and light absorption of perovskite, whilst the n-BHJ layer provides extra light absorption and charge generation to boost the short-circuit current. The combination of p-BHJ and n-BHJ CTLs in Cs 0.05 (FA 0.92 MA 0.08 ) 0.95 Pb (I 0.92 Br 0.08 ) 3 based inverted PSCs synergistically enhances the PCE from 18.3% to 22.6% with superior operational and thermal stabilities, and showing a negligible dependence on the thickness of these BHJ CTLs. Density functional theory simulations show that the formation energy of BHJ complex is critical in determining the doping effect and the ultimate performance enhancement of PSCs.

Interface engineering has become a critical process to fabricate efficient and stable planar heterojunction perovskite solar cells (PSCs), as the degradation of perovskite, hysteresis, and photo and thermal instability can all be triggered by the defective interfaces of PSCs. Herein, two fullerene derivatives, NMPPF and NMTTF, have been designed as interlayers between the MAPbI 3 and TiO 2 electron transport layer. The thiophene terminals of NMTTF have been found to effectively passivate the uncoordinated Pb 2+ of perovskite, reducing trap density and charge recombination of PSCs as well as facilitating charge transport at the perovskite and TiO 2 interface. Compared to the reference MAPbI 3 PSC with a maximum power conversion efficiency (PCE max ) of 18.7% and serious hysteresis (ΔPCE = 7.2%), PSCs incorporating NMTTF achieve a PCE max of 19.5% with minor hysteresis (ΔPCE = 1.2%) and outperform the performance of NMPPF (PCE max = 18.0%, ΔPCE = 2.3%) and PC 61 BM (PCE max = 18.9%, ΔPCE = 1.4%) modified PSCs. Unencapsulated PSCs adopting these NMPPF and NMTTF interlayers also exhibit good storage stability, maintaining 80% of their initial PCEs after storing in ambient for 30 days. This work demonstrates that the thiophene moiety can be an efficient defect passivation unit to design new fullerene molecules for interfacial engineering of PSCs with high efficiency and stability.

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Among the emerging photovoltaic technologies, organic and perovskite quantum dots (PQDs) solar cells have thrived on low-cost processing and extraordinary optoelectronic properties. Herein, CsPbBr 3 PQDs are incorporated into PM6: Y6-BO organic solar cell (OSC) to enhance device efficiency without scarifying the device stability. While the incorporation of PQDs has no impact on the molecular packing and phase separation of organic semiconductors, their presence enhances light absorption due to the Rayleigh scattering effect, promotes exciton dissociation in the Y6-BO phase, and forms an efficient hole transfer pathway from Y6-BO to PQDs and then to PM6 to improve hole transport. These contribute to increased short-circuit current density ( J SC ) and fill factor (FF) of OSCs with constant V OC . With the presence of 1 wt% CsPbBr 3 PQDs doping, the highest power conversion efficiency (PCE) of the corresponding PM6:Y6-BO OSC is improved from 16.4% to 17.1%, where the device stability has not been affected due to the better phase stability of CsPbBr 3 PQDs than CsPbI 3 PQDs. This work unravels a new approach to enhance the efficiency of OSCs by applying PQDs doping to manipulate the photon-to-electricity conversion process.