We introduce new hole-selective contacts for next-generation perovskite photovoltaics and point to design paths for molecular engineering of perfect interfaces.
The effect of sodium doping in NiO as a contact layer for perovskite solar cells is investigated. A combined X‐ray diffraction and X‐ray photoelectron spectroscopy analysis reveals that Na+ mostly segregates as NaOx/NaCl species around NiO crystallites, with the effect of reducing interface capacitance as revealed by impedance spectroscopy. Inspired by this finding, the NiO/perovskite interface in perovskite solar cells is modified via insertion of an ultrathin NaCl interlayer, which increases the NiO work‐function by 0.3 eV. This leads to an increase of power conversion efficiency, approaching 18%, and open‐circuit voltage due to a remarkable suppression of surface recombination, as revealed by photoluminescence analysis and light intensity–dependent electrical measurements.
for commercialization. [2,3] Thus, if metal halide perovskite (PSK) solar cells are to take part in supplying the world's energy demand, device stability must be significantly improved.Several kinds of stimuli have been found to degrade PSCs. When exposed to moist atmosphere, CH 3 NH 3 PbI 3 (MAPI) undergoes an irreversible degradation via the formation of hydrated phases. [4,5] Even the all-inorganic perovskite CsPbBr 3 undergoes intricate structural modifications when exposed to relative humidity (RH) above 60%, highlighting the sensitivity of lead halide perovskites to moisture also in the absence of organic cations. [6] Perovskites are also sensitive to atmospheric oxygen, which can rapidly diffuse inside the perovskite film through grain boundaries and inside the lattice via iodine vacancies. [7] Under illumination, the superoxide anion (O 2 − ) forms, which is highly reactive and triggers lattice decomposition. [8,9] Nevertheless, proper encapsulation procedures [10,11] can mitigate or, in the best scenario, eliminate the influence of moisture or oxygen on device stability. In addition to that, metal halide perovskites are also sensitive to heat, illumination, and electrical bias, three certain conditions in photovoltaic operation. In perovskite solar cells (PSCs), the interfaces are a weak link with respect to degradation. Electrochemical reactivity of the perovskite's halides has been reported for both molecular and polymeric hole selective layers (HSLs), and here it is shown that also NiO brings about this decomposition mechanism.Employing NiO as an HSL in p-i-n PSCs with power conversion efficiency (PCE) of 16.8%, noncapacitive hysteresis is found in the dark, which is attributable to the bias-induced degradation of perovskite/NiO interface. The possibility of electrochemically decoupling NiO from the perovskite via the introduction of a buffer layer is explored. Employing a hybrid magnesiumorganic interlayer, the noncapacitive hysteresis is entirely suppressed and the device's electrical stability is improved. At the same time, the PCE is improved up to 18% thanks to reduced interfacial charge recombination, which enables more efficient hole collection resulting in higher V oc and FF.
The development of scalable deposition methods for perovskite solar cell materials is critical to enable the commercialization of this nascent technology. Herein, we investigate the use and processing of nanoparticle SnO2 films as electron transport layers in perovskite solar cells and develop deposition methods for ultrasonic spray coating and slot-die coating, leading to photovoltaic device efficiencies over 19%. The effects of postprocessing treatments (thermal annealing, UV ozone, and O2 plasma) are then probed using structural and spectroscopic techniques to characterize the nature of the np-SnO2/perovskite interface. We show that a brief “hot air flow” method can be used to replace extended thermal annealing, confirming that this approach is compatible with high-throughput processing. Our results highlight the importance of interface management to minimize nonradiative losses and provide a deeper understanding of the processing requirements for large-area deposition of nanoparticle metal oxides.
A multipurpose interconnection layer based on poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), and d-sorbitol for monolithic perovskite/silicon tandem solar cells is introduced. The interconnection of independently processed silicon and perovskite subcells is a simple add-on lamination step, alleviating common fabrication complexities of tandem devices. It is demonstrated experimentally and theoretically that PEDOT:PSS is an ideal building block for manipulating the mechanical and electrical functionality of the charge recombination layer by controlling the microstructure on the nano-and mesoscale. It is elucidated that the optimal functionality of the recombination layer relies on a gradient in the d-sorbitol dopant distribution that modulates the orientation of PEDOT across the PEDOT:PSS film. Using this modified PEDOT:PSS composite, a monolithic two-terminal perovskite/silicon tandem solar cell with a steady-state efficiency of 21.0%, a fill factor of 80.4%, and negligible open circuit voltage losses compared to single-junction devices is shown. The versatility of this approach is further validated by presenting a laminated two-terminal monolithic perovskite/organic tandem solar cell with 11.7% power conversion efficiency. It is envisioned that this lamination concept can be applied for the pairing of multiple photovoltaic and other thin film technologies, creating a universal platform that facilitates mass production of tandem devices with high efficiency.
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