Ideality Factor Mapping of Back‐Contact Perovskite Solar Cells

Abstract

They enjoy high optical absorption, nearideal band gaps, high carrier mobilities, and long carrier diffusion lengths. [1][2][3][4][5][6] Meanwhile, this class of materials consists of Earth-abundant elements and is solution-processable, making it a low-cost material. [7,8] At present, sandwich structure perovskite solar cells (PSC) have demonstrated power conversion efficiencies (PCE) as high as 25.7%, only 0.4% behind monocrystalline silicon. [9] However, there has been growing interest in PSC with a back-contact architecture due to various advantages in the design compared to sandwich PSC. A key improvement is the enhanced light harvesting, due to the elimination of the front contact and its parasitic light absorption. This offers the opportunity to employ an anti-reflective coating and a front-textured perovskite layer. [6] Drift-diffusions simulations reveal an improvement in photocurrents by ≈20% [10] and with further optimization, the PCE of back-contact PSC is expected to exceed their sandwich structure counterparts. [11,12] This has already been demonstrated in the case of silicon-based devices, with champion silicon back-contact solar cells enjoying a PCE of 26.6%. [13] There has also been growing interest in PSC with a back-contact architecture as a component in tandem cells in order to exceed the Shockley-Queisser (SQ) limit of a single junction. [14,15] To date, the stabilized PCE for back-contact PSC has reached 11.5 and 9.1% for single and poly-crystalline perovskite-based devices, respectively. [16,17] While short-circuit current densities (J SC ) have exceeded 20 mA cm −2 for poly-crystalline PSC, the reported fill factors (FF) ≤ 0.56 and open-circuit voltage (V OC ) ≤ 1.06 V have been underwhelming. [17][18][19][20][21][22][23][24][25][26][27] Low FF is typically attributed to poor carrier transport and excessive recombination in the absorber layer and/or across the perovskite/transport layer interfaces. [28] Recently, our group has demonstrated that the incorporation of a mesoporous TiO 2 layer, which increases the interfacial contact area, improves charge extraction resulting in significant increases in the J SC and FF of 36 and 25%, respectively. [17] The low V OC indicates high non-radiative recombination rates. Recently, Tainter et al. [27] reported on back-contact cells that enjoy long diffusion lengths (≥12 µm), slow surface recombination velocities ≈2 cm s −1 with short circuit currents of 18.4 mA cm −2 (external quantum efficiency (EQE) of 70%) but a meager V OC = 0.57 V. They propose the limiting factor in their devices to be high dark saturation currents, a parameter that The efficiency of back-contact perovskite solar cells has steadily increased over the past few years and now exceeds 11%, with interest in these devices shifting from proof-of-concept to viable technology. In order to make further improvements in the efficiency of these devices it is necessary to understand the cause of the low fill factor, low open-circuit voltage (V OC ), and severe hysteresis. Here a time-dependent...

Enhanced Carrier Diffusion Enables Efficient Back‐Contact Perovskite Photovoltaics

“…We notice that hysteresis exists for both target and control devices, as indicated by the J–V characteristics between the reverse and the forward scans (Supporting Information, Figure S13), and the stabilized power output (SPO) measurements (Supporting Information, Figure S14). We speculate that this hysteresis is likely to be associated with the imperfect interfaces between the perovskite films and the charge selective layers, [4, 59] and/or ion migration due to the complex built‐in electric field of the back‐contact PSCs, [17, 60, 61] both of which require further investigation.…”

Interface passivation with Ti3C2Tx-MXene doped PMMA film for highly efficient and stable inverted perovskite solar cells

“…44 The ideality factor of the control devices suggests a dominance of trap-assisted monomolecular recombination, whereas PMMA:MX passivated non-radiative recombination. 45 Thus, the decrease in non-radiative recombination after the introduction of MXenes was reflected in the enhancement of V oc for PMMA:MX based devices, as shown in Table 1. n exceeding 2 for the PMMA device may be related to tail states 46 and transport losses 47 due to the high resistivity of the polymer and consequent reduced charge transport.…”

Strain Effects on Flexible Perovskite Solar Cells

“…In recent reports, some researchers employ finite element method (FEM) to simulate the stress distribution in device structures. [ 60 , 61 , 62 , 63 , 64 ] The FEM uses approximate mathematical methods to simulate real physical systems. Through simple and interacting elements, a finite number of unknowns is used to approximate a real system with infinite unknowns.…”