Polymer/Inorganic Hole Transport Layer for Low-Temperature-Processed Perovskite Solar Cells

Abstract

In the search for improvements in perovskite solar cells (PSCs), several different aspects are currently being addressed, including an increase in the stability and a reduction in the hysteresis. Both are mainly achieved by improving the cell structure, employing new materials or novel cell arrangements. We introduce a hysteresis-free low-temperature planar PSC, composed of a poly(3-hexylthiophene) (P3HT)/CuSCN bilayer as a hole transport layer (HTL) and a mixed cation perovskite absorber. Proper adjustment of the precursor concentration and thickness of the HTL led to a homogeneous and dense HTL on the perovskite layer. This strategy not only eliminated the hysteresis of the photocurrent, but also permitted power conversion efficiencies exceeding 15.3%. The P3HT/CuSCN bilayer strategy markedly improved the life span and stability of the non-encapsulated PSCs under atmospheric conditions and accelerated thermal stress. The device retained more than 80% of its initial efficiency after 100 h (60% after 500 h) of continuous thermal stress under ambient conditions. The performance and durability of the PSCs employing a polymer/inorganic bilayer as the HTL are improved mainly due to restraining perovskite ions, metals, and halides migration, emphasizing the pivotal role that can be played by the interface in the perovskite-additive hole transport materials (HTM) stack.Energies 2020, 13, 2059 2 of 12 transport materials (HTMs) have been considered so far, providing different final efficiencies, such as: (i) 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) with a PCE of 22% [6]; (ii), poly(triarylamine) (PTAA) with a PCE of 20% [7]; (iii) poly(3,4ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) with a PCE of 15% [8]; and iv) P3HT with PCE reaching 19.25% [9].There are, however, several limitations in using these kinds of materials, such as excessive price, inefficient electron-blocking capability, and low chemical stability [10]. In this respect, inorganic HTLs seem to be a convincing alternative, with materials such as NiO [11], CuI [12,13] or CuSCN [14] being potential candidates.CuSCN is a p-type inorganic semiconductor with a wide bandgap (3.4-3.9eV) [15], high hole mobility, well-aligned work function [16], good thermal stability, high optical transparency and attractive mechanical properties [17,18]. The collection of the impressive physical and chemical properties, together with its low cost and commercial availability, has made CuSCN a very suitable material to be employed as an HTL. A PCE of more than 20% has been reported for PSCs with a conventional mesostructure TiO 2 ETL and CuSCN-reduced graphene oxide (rGO) HTL [19]. However, for planar n-i-p structures, using the atomic layer deposited TiO 2 ETL and CuSCN HTL, a maximum PCE of 12.7% has been achieved so far [20]. In order to improve the open-circuit voltage in CuSCN-based PSCs, various functional molecules have been introduced between the perovskite layer and copper on the surface of CH 3 NH 3 PbI 3 layers to pass...

Impact of P3HT Regioregularity and Molecular Weight on the Efficiency and Stability of Perovskite Solar Cells

“…The final state probably achieved a better contact of the HTM with the perovskite and a better charge extraction ability . A picture of the unencapsulated device is presented in Figure S10.…”

“…The final state probably achieved a better contact of the HTM with the perovskite and a better charge extraction ability. 86 A picture of the unencapsulated device is presented in Figure S10. The morphology and the grain size of the perovskite-layer microscopy (SEM) imaging before (fresh) and after thermal stress are presented in Figure 6a−f.…”

Low‐Temperature‐Processed Stable Perovskite Solar Cells and Modules: A Comprehensive Review

“…CuSCN, CuI, and CuCrO 2 all have sufficiently high thermal stabilities. [131,132] CuI and CuSCN are strong ionic crystals, allowing the diffusion of I − and SCN − anions and causing chemical interactions with the perovskites. To overcome this issue, Ye et al demonstrated the passivation of the perovskite layer using Cu(thiourea)I to stabilize the perovskite/HTM interface.…”

Interfacial Engineering Based on Polyethylene Glycol and Cuprous Thiocyanate Layers for Efficient and Stable Perovskite Solar Cells

“…Therefore, the development of inorganic HTMs is an alternative and essential strategy for the commercialization of PSCs. [ 19–28 ]…”

“…Therefore, the development of inorganic HTMs is an alternative and essential strategy for the commercialization of PSCs. [19][20][21][22][23][24][25][26][27][28] Cuprous thiocyanate (CuSCN) has been reported to be one of the most promising inorganic HTMs with high hole mobility, excellent chemical stability, and ideal energy level alignment with perovskites. [29][30][31][32][33][34][35][36][37][38] However, compared with the devices using spiro-OMeTAD, the PSCs based on CuSCN show relatively poor photovoltaic performance, which is mainly due to the decomposition of underlying perovskites layer by polar solvents for dissolving CuSCN such as diethyl sulfide (DES), dipropyl sulfide, etc.…”